A magnetic plastic rotor disk manufacturing apparatus, includes an injection device for injecting a magnetic plastic material containing a synthetic resin matrix and a magnetic powder; a mold for molding the magnetic plastic material injected thereinto from the injection device, and a device for generating a magnetic field and magnetizing the magnetic powder in a direction along a diameter of the magnetic plastic rotor disks. The mold includes a three-plate type mold constructed of two retainer plates and a single runner stripper plate. One of the retainer plates is formed with a plurality of pin gates corresponding to the cavities so as to supply the magnetic plastic material through the pin gates into the cavities.