PURPOSE: To feed a wire smoothly by determining the upper limit of the output torque of the 2nd wire feeder within the range where no slips occur between the feed rolls of the 2nd wire feeder and the wire with a wire feeder consisting of the 1st wire feeder and the 2nd wire feeder.

CONSTITUTION: The 1st wire feeder 15 which is controlled at a constant speed is provided on welding torch side and the 2nd wire feeder 16 which is controlled at a constant torque on wire containing part side. Here, the voltage Va of an electric current detector 18 and instruction voltage Vg are compared and a phase controller 13 is operated by the differential voltage thereof, whereby the firing phase of a thyristor 20 is controlled and the upper limit of the output torque of a motor 4 is controlled within the range where no slips occur between the feed rolls 5 of the feeder 16 and a wire 14.