An electromagnetic clutch (1) is arranged on rotation axis line of a rotating member (2), and includes: output mechanism (3) containing a coil housing (31), an electromagnetic coil (32) for generating electromagnetic force, and an armature (33) supplied with restoration force in a direction in which the armature departs from the electromagnetic coil with a restoration spring (10); and cam mechanism (4) containing a control cam (41) arranged in parallel to output mechanism along a rotation axis line and incapable of rotating relative to the rotating member and a cam follower (42) capable of rolling on cam surface (330a) existing between the control cam and armature. The cam mechanism is so constructed that cam angle ¸ of the cam surface is set to an angle that makes torque applied to the armature 33 due to reaction force Fp accompanied by friction engagement with the electromagnetic coil larger than torque applied to the armature by thrust force F caused by activation of the cam mechanism.
