A solenoid of an electromagnetic clutch includes an annular coil, an annular coil housing which covers a radially facing outer peripheral surface, a radially facing inner peripheral surface and an axially facing end face of the coil. An armature is adapted to be attracted to the one end face of the coil housing by supplying an electric current to the coil. The housing axially protrudes past the other axially facing end face of the coil by a distance L. Thus, the magnetic resistance around the outer periphery of the coil is decreased to enhance the magnetic flux density of the magnetic closed circuit, thereby enabling the reliable attraction of the armature without increasing the electric power consumed by the coil.