A gear transmission mechanism includes a second gear, a first gear forming tooth portions at an outer circumference of a sector-like gear body for meshing with the second gear, and a rotation restricting mechanism for setting a rotation limit of the first gear. The rotation restricting mechanism includes an abutment portion provided in the first gear and a stopper provided in the housing. At least one of an abutment face in which the abutment portion comes into abutment against the stopper and a stopper face in which the stopper comes into abutment against the abutment face includes an inclination portion for creating a component force from rotational force of the sector gear at the time of mutual abutment.