Abstract: An electromagnetic clutch according to the present invention includes a rotor unit (11) intended to receive power from an engine of a vehicle. The rotor unit (11) has a pulley (111) around which an endless belt is passed, and a rotor (112) disposed inside the pulley (111). The pulley (111) and the rotor (112) are integrally joined together by fitting dowels (111c) projecting from an inner cylindrical surface of an inner rim (111a) of the pulley (112), into holes (112d) in an outer cylindrical surface of the rotor (112) and caulking the dowels to join the dowels and the holes (112d) together.