Q1. If an application is filed listing multiple inventors, but certain claims (and related inventors) are later deleted, is it necessary to amend the list of inventors?
A1. Generally, in Japan, it is not mandatory to delete inventors even if their related claims are removed later. As a matter of practice, all inventors involved in the initial disclosure are listed at the time of filing, and narrowing the claims during prosecution does not require amending the inventor list.
This reflects a key difference from U.S. practice: in Japan, minor inaccuracies in inventorship do not usually affect the validity of the patent. This is partly due to the view that inventions are often created in collaborative, organizational settings.
However, if you do wish to correct the inventor list by removing an individual, a signed declaration from all originally listed inventors (including those to be removed) must be submitted. The Japan Patent Office (JPO) places strong emphasis on formal procedures, so such corrections should be handled carefully.
Q2. In a divisional application, must the inventors/applicants match those listed in the parent application?
A2. No. In Japan, the inventor and applicant listed in a divisional application may differ from those in the parent.
For example, if a divisional application contains only claims relating to Invention B, it is acceptable to list only the inventors of Invention B. There is no requirement to replicate the inventorship or applicant information from the parent application.
This flexibility makes divisional applications a useful strategic tool in Japan, allowing claim sets to be reorganized and properly aligned with the appropriate inventors and applicants during the prosecution process.
Q3. Does an incorrect listing of inventors affect the validity of a Japanese patent?
A3. Generally, no.
In the U.S., errors in inventorship can lead to claims of inequitable conduct or improper ownership, potentially resulting in patent invalidation. Courts often take inventorship disputes seriously.
By contrast, in Japan, errors in the listing of inventors are rarely grounds for invalidation and seldom become a major issue in litigation. As a result, Japanese practice treats inventor designation more as a procedural formality.
However, an important exception exists: “unauthorized filings” (bōnin shutsugan), i.e., when a patent application is filed by someone who does not hold the right to obtain the patent, constitute a clear ground for invalidation under Article 123(1)(vi) of the Patent Act.
In such cases, the problem is not an incorrect inventor per se, but rather that the applicant is not a rightful successor to the person who originally held the right to the invention (i.e., the true inventor). In other words, the issue of “unauthorized filing” concerns the legitimacy of the applicant (rights holder), not merely an error in inventor listing.
To avoid this risk, it is essential to confirm who contributed to the invention and who holds the right to obtain a patent (e.g., through employment contracts, joint research agreements, etc.) before filing. Proper documentation and internal disclosure records can help establish ownership and avoid future disputes.
🔍 Practical Takeaways
- Narrowing claim sets during prosecution does not require revising the inventor list, but if correction is needed, a signed declaration from all inventors is required.
- Divisional applications in Japan may list different inventors and applicants than the parent.
- Inventor listing errors generally do not affect patent validity in Japan.
- However, unauthorized filings—where the applicant is not entitled to the invention—are clear grounds for invalidation and must be avoided through proper rights management.
