When grooves 44, 45A and 45B of an armature 42 and a rotor 43 are formed by laser beam machining, a metal oxide layer 100 is formed on wall surfaces defining the grooves 44, 45A and 45B. The metal oxide layer 100 is brought into sliding contact with a first contact surface A1 to a fourth contact surface A4 in a process in which an electromagnetic clutch is used, so that a part of the metal oxide layer 100 is ground and peeled off, whereby particles made of a metal oxide are produced. The particles enter the contact surface between the armature 42 and the rotor 43, which increases the frictional force therebetween to thereby prevent slippage. As a result, the torque transmission capability of the electromagnetic clutch M is enhanced, and the increase in the torque of a scroll compressor is achieved.