Wirings on the low-tension side which are comprised of a terminal connected to a primary winding, terminals of an electronic component, and terminals of connectors electrically connected to external devices are formed as a unit by means of a molding and formed as an insert assembly 13, and electrical connections of the respective terminals are established by welding. An arrangement is provided such that the primary winding and the insert assembly are electrically connected by fusing, are then bent and accommodated in a case.