PURPOSE: To accelerate heat dissipation by inclining the inner circumferential face of a heat dissipation hole in the direction of the heat dissipation hole at the position.

CONSTITUTION: The housing 1 is molded of a synthetic resin or made of an iron or aluminum plate, for example. A face 3 inclining in the direction of a heat dissipation hole 2 is formed on the inner circumferential side at the position of the heat dissipation hole 2 by pressing the inner face of the housing 1. Since the heat in the housing 1 flows smoothly in the direction of the heat dissipation hole 2 along the inclining face 3 and the area of inner circumferential face is increased at the position of the heat dissipation hole 2, heat dissipation is accelerated.