Abstract: A first electronic device, a second electronic device which generates less heat than the first electric device, and an electrode are connected by a heat leveling plate formed of an electrically conductive material having high thermal conductivity. A heat radiation plate is provided below an insulated substrate to which the first and second electronic devices are mounted. The second electronic device is cooled by a heat radiation path which extends through the insulated substrate and the heat radiation plate and a heat radiation path which extends through the second electronic device and the electrode to the heat radiation plate. The first and the second electronic device have substantially the same temperature due to heat radiation through the heat leveling plate. As a result, cooling effect of the electronic devices can be enhanced.