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

yes

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

1-2 years

yes. Multiple designs may be included in one design application.

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 Once the original patent application is converted, it will be deemed withdrawn.

• via Paris Convention : 12 months from earliest priority date.
• via Nationalization of PCT : 30 months from the earliest priority date.

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

10 years

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

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