PURPOSE: To improve dustproof and waterproof performance and to miniaturize the total unit, by molding for integration a bidirectional power control element and its control circuit parts as well as power circuit parts with resin on the conductive member side of an insulating high thermal conductivity substrate.

CONSTITUTION: On a conductive member 26 side of an insulating high thermal conductivity substrate 23 where the conductive member 26 is print-wired on the metal plate through an insulating thermal conductivity layer, a bidirectional power control element 18, control circuit parts of this control element 18 and power circuit parts arranged and electrically connected, and by injecting and filling epoxy resin from a resin filler hole 38 of a synthetic resin armor case 35, they are molded and secured. The connecting section 20a on the in- and output side of a power transformer as power circuit parts is projected to the conductive member 26 side and is molded and secured with resin.