Abstract: In order to increase the transfer torque by improving the level of magnetic attraction between the friction surface of an armature and the friction surface of a rotor in an electromagnetic clutch, a magnetism blocking portion for blocking a flow of magnetism is formed to extend along the circumferential direction at an approximate middle position of a disk of the armature along the radial direction. In a similar manner, a plurality of magnetism blocking portions for blocking the flow of magnetism are formed to extend along the circumferential direction at the friction surface of the rotor of the electromagnetic clutch at varying positions set along the radial direction. A plurality of magnetic poles are formed with these magnetism blocking portions, and the facing area of a given outer circumference-side magnetic pole is set smaller than the facing area of the corresponding inner circumference-side magnetic pole by forming these magnetism blocking portions at specific, appropriate positions.