PURPOSE: To improve the efficiency of a motor, by focusing magnetic flux generated by toroidal driving coils on each phase, on a toroidal inner yoke and a toroidal outer yoke.

CONSTITUTION: A toroidal magnetism-interrupting member 42 is set to come in adjacent contact with the outer periphery of an outer yoke 38, and magnetism is effectively prevented from being leaked from the outer yoke 38 to a housing 16. Besides, on the upper surfaces of a first and a second phase toroidal driving coils 28, 30, the magnetism-interrupting rings 44, 46 of conductors are arranged. In this manner, magnetic leakage in the direction of a rotor through the cut sections of yokes 32∼38 is perfectly interrupted, and on each phase, magnetic flux is focused more on the circular poles of the inner yoke 34 and the outer yoke 38, and so the efficiency of a motor is extremely improved.