To improve mountability by increasing inside space, torque transmission capacity and oil to be filled and compacting the size in an axial direction.

The electromagnetic coupling comprises a main clutch 7 for coupling a case-type torque transmission member 3 and a shaft-type torque transmission member 5, a pilot clutch 15 operated by an electromagnet 19, a cam mechanism 9 operative to couple the clutch 7 in response to torque applied to the members 3, 5 when the clutch 15 is coupled, and a rotor 25 coupled, integrally with the member 3, and forming a part of the magnetic path of the member 3. An axial-direction positioning member 59 is provided between the rotor 25 and the member 5.