PURPOSE: To provide a commutator unit in which dust does not adhere nor deposit between the end face of a commutator segment 1 and the stepped side face 8 of a cylindrical insulator 3 even if a commutator thermally expands or contracts in the commutator unit for an electric rotating machine such as a DC motor.

CONSTITUTION: In a commutator unit for electric rotating machine in which a cylindrical commutator is formed by arranging commutator segments 1 and inter-segment insulators alternately on the outer periphery of a rotary shaft 5 through a cylindrical insulator 3 and the commutator is supported on the rotary shaft through a supporting member 4, an insulating protective member 9 for hermetically sealing the stepped side face of the cylindrical insulator 3 and the end face of the commutator 1 is provided on the outer peripheral side of the cylindrical insulator 3.