A circuit device of the present invention includes a wiring board 45, and circuit elements such as semiconductor elements 32 mounted on the wiring board 45. The wiring board 45 includes: a conductive pattern 12, which is a metal core layer; a first insulating layer 14 and a second insulating layer 16 respectively covering an upper surface and a lower surface of the conductive pattern 12; and a first wiring layer 18 and a second wiring layer 20 formed respectively on an upper surface of the first insulating layer 14 and a lower surface of the second insulating layer 16. The conductive pattern 12 is made of rolled metal. With this configuration, the thermal resistance of the conductive pattern 12, which is the metal core, is reduced, and the thermal dissipation of the entire device can be improved.