A rotary actuator used in a shift-by-wire system of a vehicle includes: a motor; an output shaft arranged parallel to a rotation shaft of the motor; and a deceleration mechanism that decelerates rotation of the motor and transmits it to the output shaft. The deceleration mechanism includes a drive gear provided over a rotation axis of the rotation shaft and a driven gear provided over a rotation axis of the output shaft to mesh with the drive gear. The driven gear is a separate member from the output shaft and is loosely fitted to the output shaft.