To allow a feed pipe to follow the advancing/retracting action of the feed pipe, and to provide the sufficient connection rigidity of its portion by fixing the metal feed pipe to a base member mounted on an advancing/ retracting driving means, and press-fitting a flexible synthetic resin feed hose to a frame member fixed to the base member to keep the hose in a communicated condition with the feed pipe.

A projection nut 12 fed from a parts feeder 13 slides in a feed pipe 16 from a feed hose 15, and temporarily stops. When an air cylinder 22 is operated, the feed pipe 16 is advanced, and a screw hole of the nut is aligned with the axes of electrodes 3, 11, the advancement of the feed pipe 16 is stopped, a guide pin 5 is elevated, and the nut 12 is held in a skewered manner. When the feed pipe 16 is retracted, the nut 12 is hooked to an inclined part 8 of the guide pin, and left behind. A movable electrode 11 presses the nut 12 against a steel plate 9, and the welding current runs therein. The feed pipe 16 is firmly fixed to the base member 17, and a closed section part 20 is firmly formed of a frame member 19 and a base plate 17.