Abstract: Disclosed herein is a power module which is simple in assembly and which allows efficient release of heat generated by a converter transformer and power devices on primary and secondary circuits which are electrically separated from each other. The power module is of a construction such that a converter transformer, a primary circuit board on one side of which a part of the primary circuit of a switching power supply unit is integrated, and a secondary circuit board on one side of which a part of the secondary circuit of the switching power supply unit is integrated are three-dimensionally joined into an integral module by a resin of high thermal conduction and electrical insulation properties, the device-mounted sides of the primary and secondary circuit boards facing each other. The transformer may be placed between the two circuit boards or, alternatively, in parallel and adjacent to the two circuit boards.