body 46 is formed by the extrusion of a metallic material of aluminum or aluminum alloy the casing body 46 is of a cylindrical shape with both ends open a plurality of aligned parallel ribs 47 are formed to project from its outer circumferential surface the ribs 47 increase the surface area of the casing body 46 resulting in the increase of heat radiation as well as the rigidity and strength of the casing body 46 on the aluminum substrate 31 are mounted further devices constituting a drive control circuit such as an electrolytic capacitor 48 constituting a drive control circuit fig8 also terminal attaching plates 49 a 49 b and 49 c are connecting to the aforementioned output terminals 35 a 35 b and 36 c each signal wire of the control circuit is connected through an electric cable 51 and a coupler 52 to switches and other drive or control parts on the vehicle side output terminals 53 passing through the aforementioned output terminal holes 37 project from the lower surface of the aluminum substrate 31 such an aluminum substrate 31 and the electronic parts mounted thereon are accommodated in the casing body 46 and sealed or potted with resin 54 having the aforenoted thermal expansion characteristics as described by matching the linear expansion coefficient of the resin used to seal the semiconductor chips with that of the conductive pattern formed on the metal substrate reduces thermal stress and mechanical stress caused by the temperature cycling this achieves improvement in its durability and prevention from deterioration with a simple configuration that does not require the use a heat sink of course the embodiment described is a preferred embodiment of the invention and various changes and modifications may be made without departing from.