To reduce the cogging torque largely without reducing magnetic flux amount which contributes to torque, by involving a stator substrate with a shaft fixed, and forming a salient pole front end part shape at a stator core inner periphery into a straight shape.

At the inner periphery of a stator core 1, a driving magnet 6 retained at the outer periphery of a rotor frame 5 with a housing 4 fixed in the center, is disposed so as to face each other. A ball bearing 7 is retained in the center of a housing 4, and a rotor is supported so as to be rotated freely by inserting a shaft 9 fixed to a stator substrate 8 in the ball bearing 7. The shape of a stator core inner periphery surface shape 11 at a salient pole front end 10 of the stator core 1 is formed into a straight shape which can attain easy processing. By forming a gap between the stator core 1 and the driving magnet 6 so as to spread gradually from its center past to its end, energy change in the gap at the time of rotating the rotor is made moderate, thus enabling to reduce cogging torque largely.