PURPOSE: To provide an opening/closing apparatus for a toilet seat and a lid with limited number of parts and a lower cost by enabling the opening or closing of the toilet seat and the lid with one motor.

CONSTITUTION: A teeth-trimmed gear 3 for a toilet seat and a teeth-trimmed gear 4 for a lid are provided at the tip of a rotary shaft 2a of the toilet seat 1 and the lid 2. A retaining pawl 4a is erected on the teeth-trimmed gear 4 for the lid. A semi-circular retaining groove 3a is provided on the teeth-trimmed gear 3 for the toilet seat so that the retaining pawl 4a of the teeth-trimmed gear 4 for the lid is fitted thereinto. A belt 8 is looped on a drive wheel 6b and a driven wheel 7a and transmits a driving force of a motor 6 to a transmission gear 7. The driving force of the motor 6 is transmitted selectively to the teeth-trimmed gear 3 for the toilet seat and the teeth-trimmed gear 4 for the lid depending on the presence of the mesh of the teeth-trimmed parts of the teeth-trimmed gear 3 for the toilet seat and the teeth-trimmed gear 4 for the lid with the transmission gear 7 and the retaining of the retaining pawl 4a with the retaining groove 3a thereby opening or closing the toilet seat 1 and the lid 2.