1.　Overview

Article 17bis(3) of the Patent Act provides that any amendment of the description, etc. shall be made within the scope of the matters stated in the originally attached description, etc.  That is, Article 17bis(3) of the Patent Act provides that any new matter shall not be added.

 2. Basic Way of Thinking about Determination on New Matter

The examiner shall determine whether an amendment is an amendment which adds any new matter by determining whether the amendment introduces any new technical matter in connection with “the matters stated in the originally attached description, etc.” “The matters stated in the originally attached description, etc.” shall refer to technical matter derived by totalizing the whole statement in the originally attached description, etc. by a person skilled in the art.

3. Specific Determination on New Matter

(A) Amendment made to matters explicitly stated in the originally attached description, etc.

In the case where an amended matter is a “matter explicitly stated in the originally attached description, etc.,” because the amendment shall not introduce any new technical matter, the amendment shall be permitted.

(B) Amendment made to matters obvious from the statement in the originally attached description, etc.

In the case where an amended matter is a “matter obvious from the statement in the originally attached description, etc.,” even if the amended matter is not explicitly stated in the originally attached description, etc., because the amendment shall not introduce any new technical matter, the amendment shall be permitted.

In order to find that amended matters are “matters obvious from the statement in the originally attached description, etc.,” it is required that a person skilled in the art who contacts the originally attached description, etc. understands the amended matters as if the amended matters were stated in the originally attached description, etc., in light of the common general knowledge as of the filing.

4. Observations

In practice, claim amendments in Japan are generally perceived to be more flexibly accepted compared to those in European (EP) or Chinese patent applications. For example, even if a particular matter is not explicitly described in the specification, an amendment may still be allowed if it is clearly derivable from the drawings.

However, caution is required, as the determination of whether an amendment constitutes the addition of new matter (i.e., subject matter that goes beyond the original disclosure) can vary depending on the examiner. In cases where it is difficult to judge whether an amendment might be considered to add new matter, it can be a practical strategy to consult with the examiner and obtain informal feedback on the proposed amendment before submitting a formal response.
 

Items 1 to 3 above are excerpts from Part IV, Chapter 2 of Examination Guidelines for Patent and Utility Model in Japan, specifically the section titled Amendments Adding New Matter (Article 17-2(3) of the Patent Act).
For more details, please refer to the following link.
https://www.jpo.go.jp/e/system/laws/rule/guideline/patent/tukujitu_kijun/index.html

Japanese Patent Attorney
Yosuke Katsumi