PURPOSE: To provide coggings by notching a coil yoke on the outside of outer diameter or on the inside of inner diameter of coil arm part when a coil is arranged.

CONSTITUTION: Profile of a coil yoke 11 is notched at a rotational angle of θthus producing leakage flux intentionally between a permanent magnet 12 and the coil yoke 11. The coil yoke 11 is notched on the outside of the arm of a coil 14. Since leakage flux at a recessed part 15 on the outer periphery of the coil yoke 11 is different from that at an outer peripheral protruding part 16, flux saturation point is shifted by some rotational angle between N and S poles of the permanent magnet 12. In this case, a pole border face 13 is shifted by θ/2 rotational angle. This constitution suppresses influence of oblique flux onto the motor performance which conventionally imposed problem on the profile of a cogged coil yoke.