PURPOSE: To obtain higher transfer torque by forming permanent magnet magnetic fields of rare earth magnets and, at the same time, forming a hysteresis material rotor of a hard magnetic material having magnetic anisotropy.

CONSTITUTION: Disc-like magnetic yokes 2A and 2B are fitted and loaded into openings of both sides of a non-magnetic cylindrical case 1, and permanent magnetic fields 3A and 3B constituted of rare earth magnets such as a Nd-Fe-B system magnet, etc., are secured respectively to the inside surfaces of the magnetic yokes 2A and 2B. A rotary shaft 5 is supported by bearings 4 provided to the central parts of the magnetic yokes 2A and 2B so that it is capable of rotating, and a disc-like hysteresis material rotor 6 is secured to the rotary shaft 5. The hysteresis material rotor 6 is constituted of an anisotropic hard magnetic material having an easy magnetizing axis C in the direction of a disc-like thickness such as hard ferrite, etc.