Waste heat of a high temperature inside a main body is designed to be discharged to the outside of the main body by means of a discharge fan through a first suction air flow passage and a first discharge air flow passage. Also, through a second air flow passage communicating from a second discharge fan suction port to a discharge fan suction portion, air from the outside of the main body or air at a site of the main body, where the temperature is low, is sucked by a discharge fan so that the air of a low temperature can pass outside the drive motor to cool the latter. With this construction, the interior of the main body and the drive motor can be cooled efficiently.