https://www.epo.org/en/service-support/faq/searching-patents/asian-patent-information/japan/filing-grant/can-i-submit

Can I submit third-party observations on a Japanese patent application?

Yes. According to the Regulations under the Japan Patent Act, Article 13bis, any person may submit information at any time after a patent application or an application for a utility model is filed, or after the grant of a patent or utility model.

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