An International Guide to
Patent Case Management for Judges

7.5 Patent infringement: claim construction, doctrine of equivalents and defenses

This section outlines some key concepts that are relevant to the enforcement of patent rights in a civil lawsuit for an alleged infringement of a patent right. The following concepts are addressed: claim construction, including which materials may be used to interpret a claim, product-by-process claims and functional claims; the doctrine of equivalents; the defense of invalidity; and correction as a defense against patent invalidity.

7.5.1 Claim construction

The principles of claim construction derive from the purpose of the patent system.¹⁸³ The Supreme Court has stated that

[t]he purpose of the patent system shall be to encourage inventions and thereby to contribute to the development of the industry by granting exclusive rights (patents) to applicants who disclose their inventions. On the one hand, the patent system can protect inventions which patentees have developed. On the other hand, it facilitates the utilization of inventions by third parties through their disclosure (Patent Act, Article 1).¹⁸⁴

In this way, the patent system grants an exclusive right in exchange for the applicant’s disclosure of a patent to the public.¹⁸⁵

In patent infringement lawsuits, it is important to determine the scope of this exclusive right while balancing the protection of the patented invention and the interest of third parties to freely operate outside the scope of the patented invention.

7.5.1.1 Claim wording

Taking the purpose of the patent system into consideration, Article 70(1) of the Patent Act provides that “[t]he technical scope of a patented invention shall be determined on the basis of the statements of the patent claims attached to the application.” There is a similar principle in both U.S. and European patent law.¹⁸⁶

According to this principle, all the elements and limitations stated in the claims must be present in the defendant’s product to establish infringement. It is only when this principle is satisfied that a defendant’s product will fall within the technical scope of a patented invention. Therefore, these claims have a special status compared to other sources for interpretation. It is not possible to use elements that are not mentioned in the claims – such as from the specification and other sources – to interpret a claim more narrowly than was originally intended.¹⁸⁷ In other words, patent law provides that claims are to be interpreted according to the wording of the claims and that the wording is both the starting point and the goal.

Article 36(5) of the Patent Act provides that the applicant must state in the claims all the matters necessary for specifying the invention for which a patent right is sought. Such claims have the function of providing a third party with the most important tools to understand the content of the patented invention.

7.5.1.2 Interpreting the claims

When interpreting the wording of the claims, the standard applied is usually the natural meaning from the point of view of a person having ordinary skill in the art. The technical scope of the patented invention must be established based on the claim terms without any broadening or narrowing of their meaning.

Article 24 of the Patent Law Enforcement Regulation provides that the technical terms in the specification should be academic terms that are used in their usual sense and uniformly throughout the specification. Furthermore, the terms must be defined if they are used to indicate a specific meaning.¹⁸⁸ However, claim terms are abstract when compared to, for example, the certainty provided by a boundary line in real property. They are not defined as a particular tangible object and can be esoteric. Therefore, other materials are usually required for claim construction.

7.5.1.3 Sources for claim construction

According to Article 70(2) of the Patent Act, “the meaning of the claim terms shall be interpreted in light of specifications and the drawings.” Therefore, the detailed description of the invention in the specification and the drawings is prescribed by statute as a source for interpreting patent claims.

The prosecution file history of the patent, publicly known art, as well as common knowledge of the art can also be relevant sources for claim interpretation. Even though those sources are not provided for in statute, they are legitimate sources similar to specifications and drawings.¹⁸⁹

The key rationale for allowing non-statutory sources such as publicly known art to be used to interpret claims is disclosure to third parties: specifications and drawings are disclosed to a third party in the one document with the claims. Additionally, according to Article 186 of the Patent Act, the prosecution file history can be viewed by any third party. Further, publicly known art and common knowledge of the art is technical information that is naturally possessed by a person having ordinary skill in the art.

7.5.1.4 How to use sources

One issue in patent litigation is how all this information should be taken into consideration to properly construe the claim terms. As is the case for specifications and drawings, it is not possible to introduce elements that are not mentioned in the claims and thus to interpret the claim terms more narrowly than originally intended. However, in patent infringement lawsuits, the file history, publicly known art or common knowledge of the art can sometimes be a deciding factor when the claim construction is disputed. Establishing publicly known art and common knowledge in the art are also very important. These matters are supposed to be already possessed by persons having ordinary skill in the art, who are readers of the claims and specifications.

7.5.1.5 Product-by-process claims

Product-by-process claims can be defined as claims for inventions of products that recite the manufacturing processes of the products. The Supreme Court has stated, in a case involving this type of claim, that “[e]ven in such a case, the technical scope of the patented invention is determined as a product having the same structures and properties, which is manufactured by the described processes.”¹⁹⁰ In the same case, the Supreme Court ruled that the patents were invalid because they were contrary to the principle of claim clarity under Article 36(6)(ii) of the Patent Act and stated that such claims will conform to the principle of claim clarity only when there are circumstances where it is impossible or almost impractical to request the applicant to directly identify the product by its structure or properties. For instance, when it is technically impossible for the applicant to directly identify the object by its structure or properties, or it takes excessive economic expenditure or time to perform the identification work.¹⁹¹

Conversely, if these requirements are met, the specifications will disclose the invention of a product and not a process. In that case, it is an insufficient defense to argue that the product has been manufactured by a different process. However, in the absence of impossible or impractical circumstances, as outlined by Supreme Court above, a product-by-process claim is invalid because it runs counter to the principle of claim clarity.

Therefore, with regard to the claim wording of a manufacturing process, it cannot be assumed that all claims that contain any steps as part of a process fall within product-by-process claims. This is to be determined from a substantive and practical point of view in order not to invalidate patented inventions that have not yet been identified as product-by-process claims. In this context, it has been pointed out that, in practice, it is important to appropriately limit the scope of the application of the Supreme Court decision.¹⁹²

When the claims are determined not to be a product-by-process claim – even though they contain a manufacturing process – those processes must constitute elements or limitations in the claims so that, in accordance with the basic principle of claim interpretation, a product manufactured with a different process is not covered by the technical scope of the patented invention.

7.5.1.6 Functional claims

Functional claims are defined as claims that “are described by not concrete structures but absolute functions of the structures.”¹⁹³ An example would be when the function of glue, rather than its chemical structure, is described in the claims, using words such as “adhesive means.” As stated above, Article 36(5) of the Patent Act provides that an applicant must state in the claims all the matters necessary for specifying the invention for which a patent right is sought. Functional claims comply with this requirement and are well established in practice.

The technical scope of functional claims must be determined based on the technical idea embodied in the specific structures disclosed in the specification. This does not mean that the scope of the claims is limited to the embodiments. A structure that is not described in the embodiments but that a person having ordinary skill in the art can determine from the structure disclosed in the specification or from the detailed description of the invention is to be included in the technical scope of the invention.

It can be difficult to understand to what extent identifying particular features of embodiments is allowed. Establishing publicly known art and common knowledge in the art can help deal with this issue. These are matters that are supposed to be possessed by persons having ordinary skill in the art, who are readers of the claims and the specifications, and whose understanding is deemed to show the technical scope of the patented invention.

7.5.2 Doctrine of equivalents

There are no Japanese statutes that refer to finding patent infringement under the doctrine of equivalents. However, case law has introduced the concept of equivalence into Japanese patent law.

7.5.2.1 Five requirements of the Ball Spline Bearing Case

In the Ball Spline Bearing Case,¹⁹⁴ the Supreme Court stated that a patent can be found to have been infringed not only by a product or process that falls within the literal scope of a patent claim but also under the doctrine of equivalents. The Supreme Court set out five requirements for finding patent infringement under the doctrine of equivalents:

1. 1. The claim elements that are lacking in an allegedly infringing product or process are not essential parts of the patented invention.
2. 2. The purpose of the patented invention can be achieved, and the same function and effect can be obtained, if the lacking claim elements are replaced with corresponding parts in the allegedly infringing product or process.
3. 3. It would have been easy for a person having ordinary skill in the art to conceive of the idea of replacing the lacking claim elements with the corresponding parts in the allegedly infringing product or process at the time of the act of infringement.
4. 4. The allegedly infringing product or process was neither identical to nor easily conceived from prior art at the time the application for the patent was filed.
5. 5. No special circumstances preclude the doctrine of equivalents, such as where the allegedly infringing product or process was intentionally excluded from the scope of the claim during patent prosecution before the JPO.

The Supreme Court explained the grounds for finding patent infringement under the doctrine of equivalents in relation to these five requirements as follows:

It is extremely difficult to foresee all the types of infringements which may occur in the future and to formulate the scope of the patent claim in the specifications, and it will greatly reduce the incentive for invention in society in general if persons are able to easily avoid becoming subject to grants of injunctive relief and other exercises of rights by the patent holder by merely replacing part of the claim elements with the substance or technology which came to be known after the patent application. This would not only be contrary to the purposes of Patent Act – to the promotion of the development of industry through the protection and encouragement of invention – but would also be contrary to the principle of social justice and the idea of fairness.

Taking this into account, the substantive value of the patented invention extends to the technology which a third party can easily conceive as substantially equivalent to the construction as indicated in the scope of the patent claim in the specification, and third parties should be expected to foresee this.

On the other hand, technologies which were already in the public domain, or which a person having an average knowledge in the area of the technology used in this invention could easily have conceived at the time of the patent application, since no one could in any case have obtained a patent therefor (Patent Act, Article 29), cannot be found to fall within the technical scope of the patented invention.

Furthermore, if a patent holder has acknowledged that technology is not within the technical scope of the patent claim, or their behaviour has indicated this to be the case, for example, by intentionally excluding the technology from the scope of the patent claim during patent prosecution, the patent holder is not entitled to claim otherwise afterwards, since this is against the doctrine of estoppel.

7.5.2.2 Burden of proof

According to decisions of the lower courts that have followed the Ball Spline Bearing Case and the Grand Panel of the IP High Court in the Maxacalcitol Case (see below):

• A patentee bears the burden of proof regarding Requirements 1–3 as prescribed in the Ball Spline Bearing Case to establish patent infringement under the doctrine of equivalents.
• An alleged infringer bears the burden of proof in relation to Requirements 4–5 for denying patent infringement under the doctrine of equivalents.¹⁹⁵

7.5.2.3 Requirement 1: nonessential part

The criteria used to determine whether claim elements are essential have been the subject of case law. In the Maxacalcitol Case, the Grand Panel of the IP High Court opined as follows:

The substantial value of an invention which the Patent Act intends to protect exists in the disclosure to society of a means with a specific structure for solving a technical problem that could not have been solved by prior art, which is based on a unique technical idea that is not seen in prior art. Therefore, the essential part of a patented invention should be understood as the characteristic part which constitutes a unique technical idea that is not seen in prior art in the statements in the scope of claims of the patented invention. The aforementioned essential part should be found by first understanding the problem to be solved and the means for solving the problem of the patented invention […] and its effects […] based on the statements in the scope of claims and the specification and then determining the characteristic part that constitutes a unique technical idea that is not seen in prior art in the statements in the scope of claims of the patented invention.

The above opinion aligns with the majority of lower court decisions that have followed the Ball Spline Bearing Case.¹⁹⁶ However, this formula was not enough to resolve the issue in the Maxacalcitol Case, where the enforced patent claim required that the starting material and intermediate for producing maxacalcitol were cis-form vitamin D structures, while those used in the allegedly infringing process had trans-form vitamin D structures that were geometric isomers. That is, even after finding that the claim element was a part of the patented invention, there remained the question as to whether the cis-form was essential or not. As to this question, the Grand Panel of the IP High Court found that the cis-form was not essential, on the following grounds:

That is, taking into account that the substantial value of a patented invention is defined depending on the degree of contribution in comparison with prior art in the relevant technical field, the essential part of a patented invention should be found, based on the statements in the scope of the claim and the specification and, in particular, through comparison with prior art stated in the specification, to be in accordance with the following principle: (i) If the degree of contribution of the patented invention is considered to be large in comparison to the prior art, an essential part of the patented invention is found to be a superior concept in relation to part of the statements in the scope of claims.[…] (ii) If the degree of the contribution of the patented invention is evaluated as not much more than prior art, an essential part of the patented invention is found to be the same as literally stated in the scope of claims.

However, if the statement of the problem in the specification, which is described as one that prior art could not solve, is objectively insufficient in light of prior art as of the filing date […] prior art that is not stated in the specification should also be taken into consideration for the purpose of finding a characteristic part which constitutes a unique technical idea of the patented invention that is not seen in prior art. In such cases, the essential part of the patented invention is found to be closer to the statements in the scope of claims compared to cases where it is found only based on the statements in the scope of claims and the specification, and the scope of application of the doctrine of equivalents is considered to be narrower.

In addition, in determining the fulfillment of the first requirement, that is, whether an element which is different from the allegedly infringing product, etc., is a non-essential part, it is not appropriate to first divide the claim elements stated in the scope of claims into essential parts and non-essential parts, and then consider that the doctrine of equivalents is not applicable to all of the claim elements that fall under essential parts, but it is necessary to first determine whether the allegedly infringing product, etc., commonly has the essential part of the patented invention as mentioned above, and then consider a difference not to be an essential part if the subject product, etc., is recognized as having said essential part. Even if the allegedly infringing product, etc., has a difference which is not the characteristic part that constitutes a unique technical idea that was not seen in prior art, this fact does not become a reason for denying the fulfillment of the first requirement.¹⁹⁷

7.5.2.4 Requirement 2: possibility of replacement

The second requirement of the doctrine of equivalents is often referred to as the “possibility of replacement.” It is not always clear how or whether the function and effect of the allegedly infringing product or process can be judged to be the “same” as those of the patented invention when only allegedly trivial or immaterial differences exist. The courts have not provided any clear guidance on this issue.¹⁹⁸

7.5.2.5 Requirement 3: ease of replacement

Regarding the third requirement, such judgment needs to be made in light of the level of technology at the time of the act of infringement. Therefore, for example, if an alleged infringer’s manufacturing and distribution of an allegedly infringing product continue despite pending court proceedings, a judgment should be made based on the level of technology at the time of the closing of the oral hearings.

7.5.2.6 Requirement 4: difficulty of conception

As stated above, an alleged infringer bears the burden of proof when arguing its defense under the fourth requirement. The alleged infringer’s argument under this requirement may overlap, to some extent, with a defense based on patent invalidity due to a lack of novelty or inventive step. Under this requirement, the alleged infringer needs to establish that the allegedly infringing product or process was neither identical to nor easily conceived from the prior art while also establishing patent invalidity, which requires that the patented invention was identical to or easily conceived from the prior art.

7.5.2.7 Requirement 5: no special circumstances

The fifth requirement is that there are no special circumstances that might preclude the application of the doctrine of equivalents. A typical “special circumstance” which the Supreme Court referred to in the Ball Spline Bearing Case is where the allegedly infringing product or process was intentionally excluded from the scope of the claim during patent prosecution before the JPO. This is similar to prosecution history estoppel, which can be raised by an alleged infringer as a defense against literal infringement.

In the Maxacalcitol Case, the alleged infringer argued that there was a special circumstance preventing patent infringement from being found based on the doctrine of equivalents. The applicant had not crafted the patent claim so that it included the process where the starting material and intermediate for producing maxacalcitol had trans-form vitamin D structures, even though ordinary persons having ordinary skill in the art could have easily conceived using such a material at the time of patent filing. The Supreme Court accepted the appeal of the alleged infringer on this issue but ultimately rejected the argument:

1. (1) […] even in a situation where the scope of patent claims written by the patent applicant do not mention the structure for allegedly infringing products or processes different in part from the structure stated in the scope of claims while the applicant was able to easily conceive the structure for such allegedly infringing products or processes at the time of filing the application, the mere fact of such omission in the scope of the patent claims does not constitute a special circumstance such as where the allegedly infringing products or processes were intentionally excluded from the scope of patent claims in the course of filling the patent application.

2. (2) […] in cases where the applicant has failed to describe the structure of allegedly infringing products or processes that are different from corresponding elements of the structure stated in the patent claims, the existence of special circumstances, such as the intentional exclusion of allegedly infringing products or processes from the scope of patent claims in the course of filing an application for a patent, should be found if the applicant is objectively and visibly determined to have indicated their intention of omitting statements concerning allegedly infringing products or processes in the scope of the patent claims while recognizing that the structure for the allegedly infringing products or processes could substitute for the structure stated in the scope of the patent claims.

   In light of the facts explained in the above, nothing contained in the application for the patent indicates objectively and visibly the applicant’s intention of omitting to mention the structure for the applicant’s process in the scope of claims while recognizing that the structure adopted by the applicant, which was different in part from the structure stated in the scope of claims, could substitute for said structure.¹⁹⁹

7.5.2.8 Other relevant cases

In an early equivalence case delivered shortly after the judgment in the Ball Spline Bearing Case and prior to the establishment of the IP High Court, the Osaka High Court found indirect infringement under Article 101 of the Patent Act with respect to a product that was used exclusively for the exploitation of the allegedly infringing process. The court decided that the process for which the product was exclusively used was equivalent to the process that fell within the literal scope of the patented claim.²⁰⁰ In another, more recent case, a patentee’s right to seek compensation for the unauthorized use of a patented invention – after the publication of an unexamined application but prior to registration of the patent right under Article 65 of the Patent Act – was found to extend to the unauthorized use of products or processes equivalent to those falling within the literal scope of the patented claim.²⁰¹

7.5.3 Defense of invalidity

The defense of invalidity of a patent involves an alleged infringer asserting that a plaintiff’s patent should be invalidated.²⁰² Alleged infringers assert the defense of invalidity in about 80 percent of patent infringement cases.²⁰³ An alleged infringer may also request a JPO trial for invalidation (see Section 7.4). These trials are often conducted in parallel with a court’s determination of invalidity, and sometimes conflicting decisions are reached (see below).

Alleged infringers will sometimes adopt a strategy of not filing for a trial for invalidation because they think that a court is more likely to find invalidity than the JPO, particularly in cases in which matters of fact are contested, such as fraud, violation of the rules relating to joint applications, or publicly worked inventions. Like any other claim, the defense of invalidity of a patent will be dismissed if the assertion is not made in a timely manner or if the case would be unduly delayed.²⁰⁴

The statutory basis for the defense of invalidity was introduced by an amendment of the Patent Act in 2004 in response to a decision by the Supreme Court (Kilby Case), which held that the defense of abuse of rights could be asserted even before a trial for invalidation by the JPO becomes final and binding.²⁰⁵ While the Supreme Court’s decision in Kilby suggested that a patent would have to be invalid due to lack of inventive step to allow the defense to be raised, Article 104-3(1) of the Patent Act did not include such a restriction. However, there is no substantive difference between the level of “obviousness” required as set out in the Supreme Court decision and Article 104-3(1).

7.5.3.1 Grounds for invalidity

The grounds for invalidity that can be claimed in a defense of invalidity are violations of the following patent requirements:

• amendment requirement (addition of new matter; Patent Act, Article 17-2(3));
• novelty (Patent Act, Article 29(1));
• inventive step (Patent Act, Article 29(2));
• prior art effect (Patent Act, Article 29-2);
• enablement requirement (Patent Act, Article 36(4)(i));
• support requirement (Patent Act, Article 36(6)(i));
• clarity requirement (Patent Act, Article 36(6)(ii)); and
• usurpation (Patent Act, Article 49(7)).

Various court decisions that have addressed these grounds for invalidity are outlined below.

7.5.3.1.1 Amendment requirement (addition of new matter; Patent Act, Article 17-2(3))

In the Solder Resist Case, a Grand Panel of the IP High Court stated that

[t]he “matters described in the description or drawings” are technical matters derived by a person having ordinary skill in the art putting together all statements in the specification or drawing. If a correction introduces no new technical matter in relation to those thus derived, the correction may be deemed to be within the scope of matters described in the description or drawings.²⁰⁶

The patentee who amended the patent bears the burden of proof for this ground for invalidity.²⁰⁷

7.5.3.1.2 Novelty (Patent Act, Article 29(1))

The IP High Court has held that

[i]n order for an “invention of a product” to be described in a “publication,” it is necessary to first disclose the structure of the invention in the publication, and as the invention is a creation of technical ideas (see Patent Act, Article 2(1)), it is necessary not only to disclose the structure of the invention but also to disclose the technical ideas of the invention to the extent that a person having ordinary skill in the art who has access to the “publication” can easily work the technical ideas.²⁰⁸

The alleged infringer bears the burden of proof for this ground for invalidity.

7.5.3.1.3 Inventive step (Patent Act, Article 29(2))

In Bridgestone Co., Ltd v. Commissioner of the Patent Office, the IP High Court found that

[t]he invention of this application arranges a surface rubber layer having a low elastic modulus so that the tire can exhibit the performance on ice even in the initial stage of use, whereas the cited invention enables the body layer to exhibit the specified performance quickly by removing the surface layer by peeling easily. Therefore, the concrete problem for enabling the body layer to exhibit the performance even in the initial stage of use is different, and the technical idea of each invention’s surface layer conflicts with each other.²⁰⁹

When problems solved by the invention and a cited invention are different, such a difference is considered to support a finding of inventive step. The alleged infringer bears the burden of proof for this ground for invalidity.

7.5.3.1.4 Prior art effect (Patent Act, Article 29-2)

Requirements for this ground are:

• another application (the other application) was filed on a day earlier than the filing date of the application concerned;
• the publication of the other application occurred after the filing date of the application concerned;
• the inventor of the invention in the other application was not the same as the inventor of the invention claimed in the application concerned; and
• the applicant for the other application was not the same as the applicant for the application concerned as of the filing date of the application concerned.

The Tokyo High Court has held that

[w]here the invention claimed in the application concerned and the cited invention are different but share substantial identity, it is deemed “identity” regarding the prior art effect.

Substantial identity referred to herein means a case where a difference between the invention claimed in the application concerned and the cited invention is a very minor difference (an addition, deletion, conversion, etc., of common general knowledge or commonly used art which does not yield any new effect) in embodying means for resolving a problem.²¹⁰

The IP High Court has stated that

[e]ven if there is no particular statement in the description etc. of the prior application, the invention of the prior application can be found taking into consideration the common general technical knowledge of a person having ordinary skill in the art in order to understand the invention of the prior application. On the other hand, in the case where an invention is abstract, or technical content of an invention is insufficiently disclosed even taking into consideration the common general technical knowledge of a person having ordinary skill in the art, such invention does not fall under the “invention” mentioned above and does not have the effect of excluding the later application provided for in this Article. Further, created technical content which is not configured to the extent that any person having ordinary knowledge and experience in the art can repeatedly work the technical content to achieve an intended technical effect is not yet an “invention” and it should not be deemed that such technical content falls under “invention” as referred to in Article 29-2 of the Patent Act.²¹¹

The alleged infringer bears the burden of proof for this ground for invalidity.

7.5.3.1.5 Enablement requirement (Patent Act, Article 36(1)(i))

The IP High Court has held that

[i]n order to satisfy the enablement requirement for a process, the detailed description of the invention is required to have a description to such a degree that a person having ordinary skill in the art can use the process without requiring excessive trial and error on the basis of the contents described in the detailed description of the invention and the common general technical knowledge as at the time of filing, and the presence of the description to such a degree is sufficient.

In order to satisfy the enablement requirement for a product, the detailed description of the invention is required to have a description to such a degree that a person having ordinary skill in the art can make the product without requiring excessive trial and error on the basis of the contents described in the detailed description of the Invention and the common general technical knowledge as of the time of the filing.²¹²

The IP High Court has also held that

[i]n order to fulfil the enablement requirement for a process for producing the product, the detailed description of the invention is required to have a description to such a degree that a person having ordinary skill in the art can use the process and also can use the product produced by the process without requiring excessive trial and error on the basis of the contents described in the detailed description of the invention and the common general technical knowledge as of the time of the filing.²¹³

The patentee bears the burden of proof for this ground for invalidity (as long as it is the same patent that is the subject of an invalidation trial before the JPO (common view)).

7.5.3.1.6 Support requirement (Patent Act, Article 36(6)(i))

In the Polarizing Film Manufacturing Process Case, a Grand Panel of the IP High Court held that

[c]laim recitations are first compared with the detailed description of the invention; then the fulfillment of the Support Requirement is determined according to whether the claimed invention was described in the detailed description of the invention, whether a person having ordinary skill in the art could have solved the problem of the claimed invention based on its recitations, or a person having ordinary skill in the art could have solved the problem of the claimed invention based on common technical knowledge at the filing date given that the recitations were not included nor suggested in the detailed description of the invention.²¹⁴

The patentee bears the burden of proof for this ground for invalidity (as long as it is the same patent that is the subject of an invalidation trial before the JPO (common view)).

7.5.3.1.7 Clarity requirement (Patent Act, Article 36(6)(ii))

The IP High Court has held that

[Article 36(6)(ii) of the Patent Act] was established in view of the fact that, if the invention presented in the claims is not clear enough, the technical scope of the invention protected by the patent would be unclear and could cause unexpected disadvantage to third parties. The objective of this provision is to prevent such inconvenience. A determination as to whether or not the invention claimed in a patent application is clear should be determined based not only on the information presented in the claims but also on the information presented in the description and drawings attached to the patent application. Moreover, that determination should be made from the perspective of whether the information presented in the claims can be considered to be so unclear that it would make third parties suffer unexpected disadvantages in light of the common general technical knowledge of persons having ordinary skill in the art as of the time of the filing of the application.²¹⁵

However, the IP High Court has also held that

[e]ven if a process for manufacturing a product is described in the scope of claims for a product, if it is clear from the scope of claims, description, drawings, and common general knowledge that the structure or properties of the product are represented by the process, the benefit of a third party is not unreasonably harmed, and therefore, it does not constitute a violation of the clarity requirement.²¹⁶

The patentee bears the burden of proof for this ground for invalidity (as long as it is the same patent that is the subject of an invalidation trial before the JPO (common view)).

7.5.3.1.8 Usurpation (Patent Act, Article 49(7))

The IP High Court has held that

[i]n a trial for patent invalidation requested on the grounds of a usurped application, it is the patentee that bears the burden of allegation and proof in relation to the fact that “the patent application was filed by the inventor of the invention for which a patent was sought or by a person to whom the right to obtain a patent was assigned from the inventor.” Even if such interpretation is adopted, it would not mean that the patentee of an invention who faces such a trial is always required to present independent, specific, concrete, and detailed allegations and proof with regard to how the invention was made. The required breadth and depth of the patentee’s allegations and proof should be determined based on the nature of the specific grounds that allege that the patent was granted based on a usurped application and also based on the breadth and depth of the allegations and proof of the person who requested a trial for invalidation, and also that, if the person who requested a trial for invalidation fails to provide any specific grounds to allege that the patent was granted based on a usurped application and also fails to provide any evidence for such allegation, the patentee is merely required to provide relatively simple allegations and proof. Whereas, if the person who requested a trial for invalidation provides specific grounds to allege that the patent was granted based on a usurped application and also provides evidence for such allegation, the patentee cannot be considered to have fulfilled the burden of allegation and proof unless the patentee provides allegations and proof that outweigh the allegations and proof provided by the former person.²¹⁷

The alleged infringer bears the burden of proof for this ground for invalidity. However, for this ground, the burden of proof will pass to the patentee if the appellant of a trial for invalidation identifies circumstances in support of usurpation.²¹⁸

7.5.3.2 Parallel Japan Patent Office trial for invalidation

As noted above, an alleged infringer may request a JPO trial for invalidation in addition to asserting the defense of invalidity in a patent infringement lawsuit. JPO trials are frequently conducted in parallel to a court’s proceedings, and conflicting decisions are sometimes reached. However, an invalidity determination by the court affects only the parties and therefore does not invalidate the patent with respect to third parties. Only the JPO can invalidate a patent with erga omnes effect.

When a JPO trial for invalidation results in a decision that a patent is invalid, and that decision become final and binding, the patent is invalid for the parties and any third parties. Therefore, the patent will also be invalid for the purpose of a patent infringement lawsuit, and so the case will be decided against the patentee.

When a JPO trial for invalidation results in a decision that a patent is valid and should be maintained, and the decision becomes final and binding – and the defendant does not appeal the JPO decision to the IP High Court – it will be impossible to assert a defense of invalidity on the same grounds in a patent infringement lawsuit. This is because it would be a violation of the doctrine of good faith and fair dealing.²¹⁹ Therefore, if an alleged infringer in a patent infringement lawsuit is not successful in a parallel JPO trial for invalidation, the alleged infringer must appeal to the IP High Court.²²⁰

7.5.3.3 Limitations on assertions in retrials

In patent infringement proceedings, a defendant may assert a defense of invalidity, and a plaintiff may assert a defense of correction, and both parties will present their views as to the validity and scope of the allegedly infringed patent. However, there is the potential that a JPO decision in a trial for invalidation or a trial for correction – that differs from the judgment in a patent infringement lawsuit in relation to the validity and scope of a patent – becomes final and binding after the judgment in the patent infringement lawsuit becomes final and binding, thereby reversing that judgment. Thus, in 2011, the Patent Act was amended to impose certain limitations on the assertions that may be made in a retrial under Article 338(1)(viii) of the Code of Civil Procedure (when a civil judgment has been modified by a subsequent administrative decision).

Article 104-4 of the Patent Act provides that if a JPO trial or appeal decision – that a patent is to be invalidated or corrected – becomes final and binding after a final judgment in a patent infringement lawsuit becomes final and binding, a person that was a party to the patent infringement lawsuit may not assert that JPO trial or appeal in a retrial of the final decision in the patent infringement lawsuit, including in any action claiming compensation for damages and restitution for unjust enrichment.

For example, a person who has been found liable for infringement in a patent infringement lawsuit cannot, in a retrial of the lawsuit, demand the return of compensation for damages or restitution paid if the JPO later finds the patent to be invalid. In these circumstances, an injunction order issued in a patent infringement lawsuit would no longer be effective because the basis for infringement would have disappeared. Any compensation or restitution already paid cannot be reclaimed.

In addition, although not originally envisaged by Article 104-4, the IP High Court has held that

because the Patent Act provides that an alleged infringing item that does not fall within the technical scope of the patent invention before a correction does not fall within the technical scope of the patented invention after a correction, an allegation by a patentee in a retrial that an alleged infringing item falls within the technical scope of the patent invention as a result of a JPO decision upholding a correction but after a judgment that dismissed the request on the grounds that the alleged infringing item did not fall within the technical scope of the patent invention, is not envisaged by the Patent Act.²²¹

Therefore, an alleged infringer must strongly argue the defense of invalidity, and a patentee must strongly argue the defense of correction in patent litigation proceedings. Otherwise, even if a favorable JPO trial decision becomes final and binding after the judgment of a court in a patent infringement lawsuit becomes final and binding, the judgment of the latter may not be reversed in a retrial.

7.5.4 Defense of correction

When a defense of invalidity is asserted by a defendant in patent infringement proceedings, the plaintiff (the patentee) may be able to avoid invalidity by asserting a defense of correction – that the grounds for invalidity can be addressed by either a final and binding JPO correction decision or a request for a correction. Therefore, in parallel with this, the alleged infringer can assert the effect of the correction in a suit for infringement of a patent.

7.5.4.1 Four requirements and an exception

The following four requirements must be satisfied for a defense of correction:

• The request for correction (where a trial for invalidation is pending) or the request for a trial of correction by the JPO (where a trial for invalidation is not pending) must be lawful.²²²
• The correction meets the correction requirements – that is, no new matter has been added.
• The reason for invalidation alleged in the defense of invalidity is resolved by the correction.
• The defendant’s product (or process) falls within the technical scope of the patented invention after correction.

However, in relation to the first requirement, under the Patent Act, there is period in which a request for neither a correction nor for a trial for correction can be made, and so the IP High Court has ruled that

when it is legally difficult for a patentee to file a request for correction etc., such circumstances should be taken into consideration on a case-by-case basis from the standpoint of fairness, and when there are special circumstances that do not require the filing of a legal request for correction etc., the patentee may be allowed to make an allegation of defense of correction without satisfying such requirement.²²³

In this regard, the IP High Court has held that

if such request cannot be made because the patentee’s right to request correction or request a trial for correction is restricted, a declaration to the effect that such request for correction (or a request for a trial for correction) will be made when it “becomes possible” is sufficient.²²⁴

In addition, the IP High Court has also held that

the appellant could request neither a correction nor a trial for correction until receiving a notice of the trial decision from the JPO under Article 126, paragraph (2), Article 134-2, paragraph (1) of the Patent Act. Under such circumstances, the appellant does not need to make these requests to the JPO in order to assert the defense of correction.²²⁵

Accordingly, it is still possible to assert the defense of correction even during the term when it is not possible to request a correction or a trial for correction under the Patent Act. However, the patentee will need to request a correction or trial for correction at the JPO when it becomes possible to do so under the Patent Act.

A patentee is required to assert a defense of correction before the conclusion of the oral hearing of the IP High Court at the latest so as not to cause a delay, irrespective of the progress of the hearing proceedings before the JPO. Otherwise, it will be impossible to assert a defense of correction when a correction or a trial for correction may be requested under the Patent Act.²²⁶ A patentee should be mindful of this timing issue.

7.5.4.2 When to assert the defense

The defense of correction will be dismissed if it is late or if it will unduly delay the proceedings.²²⁷ For example, the IP High Court has dismissed a defense of correction submitted four days before the first hearing date of an appeal trial because “it was possible to the assert the defense of correction by the due date of the first brief before the IP High Court.”²²⁸

7.5.4.3 Consent of joint owner and exclusive licensee

Under the Patent Act, a patentee may only request a trial for correction with the consent of any joint owners and exclusive licensees.²²⁹ Further, the Tokyo District Court has also rejected a patentee’s defense of correction assertion to which a nonexclusive licensee did not consent.²³⁰

7.5.4.4 Patentee failure to request correction or trial for correction

As noted above, the defense of correction usually requires that a lawful request for correction or a trial of correction has been made with the JPO.²³¹ However, the IP High Court has indicated that this is not necessary during the period when neither a correction nor a trial for correction may be requested under the Patent Act. In these circumstances, the patentee is required to file a request for correction or a trial for correction at the JPO when it becomes possible to do so under the Patent Act.

However, there is a risk that this could lead to complexity and undesirable outcomes. For example, it could lead to a situation wherein a patentee asserts the defense of correction (without first requesting a correction or a trial for correction) and is successful in a patent infringement lawsuit as a result of asserting this defense but does not request a correction or a trial for correction with different claim wording with the JPO, even when it becomes possible to do so under the Patent Act.

There is some debate as to the type of penalty that could be imposed on the patentee in such a situation and whether a defendant could seek a retrial of a patent infringement lawsuit that has already become final and binding. However, there are no court cases that consider this point, and the debate is still developing