To stop the rotation of an electromagnet for an electromagnetic coupling disposed between rotation shafts such as propeller shafts with a simple structure and at a low cost.

This electromagnetic coupling 1 is disposed between rotation shafts and supported by a car body through a support member 49 and a bearing 51, and controls transmission torque by the electromagnet 3. In this case, a detent member 15 separated from the support member 49 is so formed that a core 97 of the electromagnet 3, the support member 49 and the detent member 15 can not relatively rotated with respect to one another.