PURPOSE: To cool a device and put brush abraded-powder outside to prevent insulation from being deteriorated, by using a plurality of brush inspecting apertures arranged on a frame, and by enabling atmospheric air to be sucked in the frame.

CONSTITUTION: On a frame 10 for covering an armature, six brush-inspecting apertures 11 are arranged at equal intervals, and to one brush-inspecting aperture 11a, a pipe 13 communicated with a blower unit 12 is connected. A brush inspecting aperture 11b on the side opposite to the brush inspecting aperture 11a with the connected pipe 13 is provided with a vent hole 14. The vent hole 14 is provided with a mesh filter so that dust cannot be infiltrated through, and the other brush inspecting apertures 11 are provided with side plates 15. At the time of operating a motor, the blower unit 12 is started, and through the vent hole 14, atmospheric air is sucked into the frame 10 to cool the armature.