show a first embodiment according to the present invention fig1 a being a side view in vertical section fig1 b being a front view in vertical section of the same that is fig1 a and 1b show a three pole type outer rotor stepping motor having a rotor 1 constituted by a ring of permanent magnet material and a stator 2 disposed in the inside of the rotor 1 the inner circumference of the ring like rotor 1 is magnetized to form n and s poles alternately disposed at equal pitches the number of each of the n and s poles is zm although n and s poles are shown on the end surface of the ring 1 in fig1 a it is a matter of course that those poles n and s are magnetized in the inner circumferential surface of the ring like rotor 1 actually the three phase stator 2 is provided with three magnetic poles 2 1 2 2 and 2 3 which are arranged at equal pitches of 120 u00b0 a plurality of teeth are provided on the top end of each of the magnetic poles 2 1 2 2 and 2 3 of the stator 2 the number of the teeth is selected to be equal between the respective magnetic poles 2 1 2 2 and 2 3 of the stator 2 and the pitch of the teeth of each of the magnetic poles 2 1 2 2 and 2 3 of the stator 2 is selected to be equal or approximate to a value of 360 u00b0 zm the stator 2 is provided with three coils 3 for three phases which are wound respectively on the three magnetic poles 2 1 2 2 and 2 3 of the stator 2 the motor.