PURPOSE: To automatically achieve the arc welding without any special technique by preliminarily providing the bending habit to a welding wire corresponding to the manipulation, and proceeding the welding while the welding wire is automatically moved along the welding position.

CONSTITUTION: When a welding wire 10 is fed while ejecting the shield gas and the welding current is applied, the waved welding wire 10 is fed while being bent according to the wave which is provided from the timepoint after the tip of the contact tip, and the arc is generated between the welding wire 10 and a deformed reinforcement close to a U-shaped copper backing 4. The welding current is detected, and the output of the wire feeding speed or the like is controlled by the sequence control, the waveform control and the inference based on the fuzzy inference so that the current value may be constant. The stable welding bead can be formed and accumulated thereby.