A double-sided circuit board including a substrate having a first surface and a second surface on an opposite side of the first surface and having a penetrating hole extending between the first surface and the second surface, a first conductive circuit formed on the first surface of the substrate, a second conductive circuit formed on the second surface of the substrate, and a through-hole conductor formed in the penetrating hole of the substrate and electrically connecting the first conductive circuit and the second conductive circuit. The penetrating hole comprises a first hole having a first opening with a diameter R1 on the first surface of the substrate, a second hole having a second opening with a diameter R2 on the second surface of the substrate, and a third hole connecting the first hole and the second hole and having a diameter smaller than at least one of R1 and R2.