To improve the mechanical strength of a plastic magnetic molded piece and make the press-fitting width for a rotor using it to be larger.

A plastic magnet molding is formed plastic magnet molded material to which a reinforcing material made of carbon fiber or glass fiber, etc., in addition to magnetic powder and resin binder is added, so as to improve its mechanical strength. The addition of the reinforcing material causes a slight decrease in its magnetic property, hoever, when a magnetic powder with high magnetic property containing rare-earth metal and Co is used therefor, it hardly gives any influence to devices. After rotor magnetic 1 which is cylindrical substantially by using a plastic magnet molding is molded, a central shaft 2 is press-fitted into a central hole so as to form a rotor. At this time, any cracking due to press-fitting, especially cracking in an anisotropic direction in case of an anisotropic magnetic is hardly generated, so that the press-fitting width can be made smaller and its slip torque be also made larger.