Which is the competent authority for utility model patent applications in Japan?

yes

Inventors have a novelty grace period of 12 months after disclosure (including sale).

25 years

yes.

• Within 3 years from the filing date, the patent type can be changed from utility model to invention upon request of the applicant
• Utility model patents can be converted to design patents at any time

A conversion fee shall be paid for patent type conversion. Once the original patent application is converted, it will be deemed withdrawn.

Inventors have a novelty grace period of 12 months after disclosure (including sale).

1-2 years

• via Paris Convention : 6 months from earliest priority date.
• Hague Agreement route: 6 months from earliest priority date.

Reinstatement of priority on grounds of "due care" accepted.

yes. Within 3 years from the date of application, or within 3 months from the date of receipt of the rejection decision, the patent type can be changed from design to invention/utility model at the request of the applicant.

A conversion fee shall be paid for patent type conversion. Once the original patent application is converted, it will be deemed withdrawn.

Japan Patent Office

English: Japan Patent Office, abbreviation: JPO

Website: Japan Patent Office (jpo.go.jp)

Japanese Utility Model Patent Search: Japan Platform for Patent Information｜J-PlatPat [JPP] (inpit.go.jp)