PURPOSE: To prevent occurrence of a difference in the height between adjacent commutator bars and a crack of synthetic resin, to enable smooth rotation of a commutator and thereby to improve the reliability of a motor.

CONSTITUTION: A projection 2 is provided on the surface of the outer periphery of a commutator bar 1. As to dimensions of the projection 2, the cross-sectional area thereof is calculated from a compressive force being necessary at the time of molding and from a yield stress of the projection 2 and a proper shape is determined. Then, the commutator bar 1 and an insulating piece 4 are assembled alternately and pressed in a ring 5 for molding and they are molded monolithically with synthetic resin. Besides, a gap 6 of a dimension allowing the projection 2 to be deformed at the time of pressing in is left. After a commutator is taken out of the ring 5 for molding, the outer periphery of the commutator 1 is subjected to cutting so as to cut the projection 2.