An electronic part mounting heat-dissipating substrate which includes: a conductor plate which is formed on lead frames of wiring pattern shapes; and an insulating member which is provided between the lead frames of the wiring pattern shapes on the conductor plate; wherein a plate surface of a part arrangement surface of the conductor plate and a top surface of the insulating member at a side of the part arrangement surface form one continuous surface, wherein a plate surface of a back surface of the part arrangement surface of the conductor plate and a top surface of the insulating member at a side of the back surface at the part arrangement surface-side are formed in an identical plane, wherein the substrate is formed in a circular shape