PURPOSE: To improve heat dissipation and to reduce the number of parts by extending a metal core from an insulating layer, by bending it, and by using the wiring board itself as a structure part of a boxed body.

CONSTITUTION: A metal core 12A is extended to both sides of an insulating layer 14A, and an extension part thereof is bent above at approximately a right angle. Therefore, rigidity of the metal core 12A increases and can be used as a part of a structure member of a boxed body. A bolt hole 32 is formed at each of four corners of the metal core 12A. Each metal core printed wiring board 10A is overlaid with the bolt hole 32 and joined mutually by a long bolt 34. Thereby, a heat dissipating area increases, heat dissipation is improved and the number of parts can be reduced.