PURPOSE: To facilitate the security of the insulation property of a metal fitting part at the time of having electrically abutted and fixed a plate, where a negative holder is fixed directly, to the bottom of a metallic end bracket at earth potential by providing a recessed groove at the bottom of the end bracket opposed to the metal fitting for fixing an insulating plate and a positive brush.

CONSTITUTION: A positive brush holder 5b is fixed to an insulating plate 8 by a metal fitting 9. And, a recessed groove 1a is provided coaxially with a bearing 11, at the bottom of the metallic end bracket 1 opposed to the metal fitting 9. Accordingly, the positive brush 4b and the positive brush 5b are insulated from earth potential by the insulating plate 8. Moreover, the metal fitting 9 secures the insulation distance by the round hole 2a provided in the metallic plate 2 and the recessed groove 1a of the end bracket 1, and it is insulated from earth potential. Hereby, the metal fitting part and the metallic end bracket can easily be insulated.