To dispense with a special component for radiation of heat and to obtain the heat radiating effect with a simple means by fixing a semiconductor element for controlling the winding current of a motor to a disc-shaped bottom inner face of a motor holding cylindrical portion integrally connected with a cylindrical wind tunnel part by a plurality of legs.

A shallow recessed portion is formed on a disc-shaped bottom portion 1-7, and a screw member 8 is used as a securing and fastening means of a semiconductor element 5-2. A point of the screw member 8 is prevented from brought into contact with a name plate 7 affixed as a covering member. A window 1-8 leading inside of the disc-shaped bottom part 1-7 is formed, and a leg connecting a wind tunnel portion of a venturi case 1 with a motor holding cylindrical portion 1-6 comprises a leader line insertion groove 1-5. By bringing and fixing the heating semiconductor element 5-2 to the motor holding cylindrical portion 1-6 integrated with the veturi case made of a metallic member, the radiation can be effectively performed.