<p>An electromagnetic clutch, comprising a rotor unit (11) receiving a power from the engine of an automobile. The rotor unit (11) comprises a pulley (111) around which an endless belt is wrapped and a rotor (112) disposed in the pulley (111). The pulley (111) and the rotor (112) are integrally connected to each other by fitting a small projection (111c) projected from the inner peripheral surface of the inner rim (111a) of the pulley (111) to a hole (112d) formed in the outer peripheral surface of the rotor (112) and caulking the small projection against the hole (112d).</p>
