A sun gear is supported by an eccentric portion of a rotor via a bearing and rotatable eccentrically to the rotor axis. A ring gear includes inner teeth via which the ring gear is meshed with outer teeth of the sun gear. An output shaft is located adjacent to the sun gear in the axial direction. A fitted portion of the output shaft is loosely fitted to a fitting portion of the sun gear to transfer rotation of the sun gear to the output shaft. The bearing has a center position located in a fitting overlap region between the fitting portion of the sun gear and the fitted portion of the output shaft in the axial direction and/or located in a gear overlap region between the outer teeth of the sun gear and the inner teeth of the ring gear which are meshed with the outer gear.