A socket portion is provided to project from one side surface of a transformer receiving portion to thereby form a body case, and a lighting transformer is received in the transformer receiving portion so that a high voltage side output end of a secondary coil of the lighting transformer is electrically connected to a terminal provided in the socket portion and a primary coil of the lighting transformer is connected to an external electric path directly or through a circuit portion. Accordingly, the transformer receiving portion and the socket portion are integrally formed with each other to thereby form a unit structure.