After respective one ends of lead wires are fixed to a printed circuit board, the lead wires are bent, the printed circuit board is brought into a case and the other ends of the lead wires are bonded to terminals of the case. Since the lead wires are processed before the substrate is brought into the case, this eliminates the necessity to perform formation of the bent portions of the lead wires and fixing of the lead wires to the substrate in a narrow space of the case and allows simplification of bonding operation. Thus provided is a lead wire bonding method for bonding lead wires with bent portions to the substrate, which simplifies a bonding operation.