The terminal portion 83 of a contact 82 is of a groove type, with a larger diameter than the lead wire diameter, and includes small holes 84 drilled and installed in the bottom of the groove. By such a construction, when the solder 19 flows in between the terminal portion 83 and the lead wire by the surface tension, the air between the terminal portion 83 and the lead wire discharges through the small holes 84, thus preventing formation of an air layer between the terminal portion 83 and the lead wire. The holes 84 permit solder to enter the holes to discharge the air, but are sufficiently small to prevent solder from flowing therethrough and dripping out of the groove. By observing whether or not the solder has flowed into the small holes 84 it is possible to confirm whether the solder has entered the clearance between the lead wire and the terminal.