The present invention is used with a stopper mechanism for mechanically stopping the rotation of a motor. A pair of brushes is disposed such that a line which passes through the center of a rotor and connects the centers of the paired brushes is offset by a predetermined angle from a line which connects the centers of paired magnets. A commutator is disposed in such a manner as to be offset from a reference position by the same angle as the predetermined angle by which the paired brushes are offset. The predetermined angle falls within a range between an angle obtained by dividing 70° by the number of pairs of stator poles and an angle obtained by dividing 290° by the number of pairs of stator poles. Specifically, in the case of two stator poles, the predetermined angle falls within a range of 70° to 290° inclusive. In the case of four stator poles, the predetermined angle falls within a range of 35° to 145° inclusive.