An insulation displacement connector (40) selectively effects insulation displacement of required conductive paths of a flat cable (30) in correspondence with the function of a bulb socket connector (20). Further, the other unnecessary conductive paths are passed through without being subjected to insulation displacement connection. In addition, as the insulation displacement connector (40) and a socket housing with a bulb (21) fitted thereto are engaged, insulation displacement terminals and bulb conductor portions of the bulb (21) are electrically connected directly.