Since centers of a second gear, a fourth gear and a sixth gear coincide with each other and are disposed rotatably round a circumference of the same long shaft, a compact configuration can be realized while using a gear train of five gears to obtain a reduction gear ratio of a high gear ratio. The configuration in which the three gears have the same rotational center shaft in the way described above in an actuator which incorporates a plurality of gears is advantageous in that the number of center shafts is reduced and that the number of supporting holes in a housing which support center shafts is reduced.