To suppress magnetic force leakage from an electromagnet and ensure efficient connection and disconnection of a pilot clutch.

The coupling comprises a case-type torque transmission member 3 and a shaft-type torque transmission member 9, a main clutch arranged between the torque transmission members, a pilot clutch 19, an electromagnet 51 and an armature 53 for coupling the pilot clutch 19, a rotation member 31 made of magnetic material, rotating integrally with the case-type torque transmission member 3, and forming a part of a magnetic circuit, a cam mechanism 13 operative to the main clutch 11 via a pressing member 15 in respond to transmission torque of the torque transmission members 3, 9 when the pilot clutch 19 is coupled. A cap 71 made of non-magnetic material is arranged between the pilot clutch 19 and the case-type torque transmission member 3.