An electronic component is mounted on one major surface of a dual side wiring substrate. A terminal is press-fitted into a mounting hole in the dual side wiring substrate from the one major surface side to be temporarily fixed in the substrate, and an electronic component is mounted on the other major surface of the dual side wiring substrate after soldering paste is applied. A frame having a plurality of bent pieces extending inwardly is mounted onto the dual face wiring substrate from a position above the substrate so that the bent pieces abut against the pattern of the dual side wiring substrate. The terminal press-fitted from the one major surface side, the electronic component mounted on the other major surface, and the frame are soldered simultaneously by a reflow method.