PURPOSE: To enable a rotary shaft to be always rotated in a non-contacted state by holding a permanent magnet, which is equally divided inside at the center in the width direction of a yoke, between the inner surface of the yoke and the back surface of an inside magnetic pole, disposing an exciting coil in such a manner as to surround the leg of the inside magnetic pole, and providing outside magnetic poles, where magnetic poles are divided, on both sides of the yoke.

CONSTITUTION: A permanent magnet 3, which is divided into a plurality of pieces inside at the center in the width direction of a yoke 1, is held between the inner surface of the yoke 1 and the back surface of an inside magnetic pole 4. An exciting coil 5 is disposed in such a manner as to surround the leg of the inside magnetic pole 4 adjacent to the permanent magnet 3, thus obtaining an electromagnet. An outside magnetic pole 2, into which a rotary shaft 10 is inserted, is provided on both sides of the yoke 1. A plurality of magnetic poles defined by grooves 7 extending from the hole are formed in the outside magnetic pole 2. A magnetic circuit is constituted of the inside magnetic pole and the outside magnetic pole. Thickness of the back surface of the inside magnetic pole and a clearance between the back surface and the outside magnetic pole are varied so that attraction force of the permanent magnet can be changed.