To constitute a simple control circuit which applies a voltage for exciting each coil.

Dual-purpose exciting and anti-exciting coils of magnet assembling bodies 7, 8 are divided into exciting coils 35, 40 and anti-exciting coils 36, 41 which are wound over in different directions each other. The exciting coil 35 of the magnet assemblying body 7 of the brake side and the anti-exciting coil of the magnet assemblying body 8 of the clutch side are connected to a single control circuit 50 and a voltage is simultaneously applied to them and the antiexciting coil 36 of the magnet assemblying body 7 of the brake side and the exciting coil 40 of the magnet assemblying body 8 of the clutch side are connected to a single control circuit 60 and a voltage is simultaneouly applied to them.