To transmit a rotating force from a drive source at a high reduction ratio without enlarging the device.

A single epicyclic gear 21 is geared with an output gear 16 and a fixed gear 14, which are coaxially disposed and have different numbers of teeth, respectively. At least, one of the fixed gear and the output gear is constituted of a profile-shifted gear so as to equalize the gearing pitch circles of the fixed gear and the output gear. When an outer rotor 18 rotates, the epicyclic gear epicyclically rotates while gearing with the fixed gear and the output gear. The output gear rotates thereby, the rotating force is transmitted to the output shaft 11, and a driven object rotates at a prescribed rotation speed. A reduction ration then is obtained based on the difference in the number of the teeth of the fixed gear and the output gear and is independent of the number of the teeth of the epicyclic gear. When obtaining the reduction ratio of 1/20, it can be obtained by setting, for example, the number of the teeth of the output gear to 40, the number of teeth of the fixed gear to 38, and the number of the teeth of the epicyclic gear to 19.