A circuit board includes a substrate having a pair of pads at mutually opposite positions of a front surface and a rear surface of the substrate; a circuit element having a heat dissipation part which is soldered to one of the pair of pads; and a heat transfer section which pierces through the substrate in a thickness direction, and both ends of which are soldered to the pair of pads respectively, wherein at least a part of the heat transfer section has a solid structure which prevents air from passing through between the front surface and the rear surface.