A circuit device includes a metal substrate; and a plurality of circuit elements, mounted on the metal substrate, which electrically connects to the metal substrate. The metal substrate is made of a copper plate of high thermal conductivity. The metal substrate is demarcated into a plurality of sections by insulating films added with a filler for enhancing the thermal conductivity in resin. The circuit elements, which have respective independent operating potentials on a side of the metal substrate of the circuit elements, are respectively provided on separated copper plates.