Abstract: A rotor is manufactured by disposing a commutator integral with a rotary shaft centrally within a casting jig, arranging a rotor coil around the commutator, and integrally molding the assembly in synthetic resin. The rotor coil comprises a coil wound on a bobbin formed with positioning openings. Guide pins are provided within the jig in the region of the rotor coil for fitting engagement with the positioning openings in the latter. When molding the rotor, the rotor coil is properly positioned as a result of the engagement between the guide pins and the mating openings, assuring the molding of a balanced rotor.