The brush guard (10) has a carbon frame (11) and the composite carbon layers arranged in facing surfaces in a contact portion (18) with respect to terminal guard side separated by an insulation layer. The contact portion is provided with contact section having axis parallel to commutator axis (28). The height of contact portion is set to 4.5-5.5 mm while the width is set to 2.8 times the height of contact portion in vicinity of commutator.
