PURPOSE: To unify setting of welding conditions and select adequate conditions by providing a setter for welding current, a signal converter for welding voltage, a detector for welding voltage, control circuits for pulse and base voltages, and a converter and a control circuit for wire feed speed.

CONSTITUTION: The material of base metals and the diameter of a wire are set with a switch 24, and an adequate current value is set with a setter 14 for welding current, thereafter a welding machine is started. Then the voltage signal Vi from the setter 14 is converted to a welding voltage signal Ve and a wire feed speed signal Vf. The signal Ve is distributed to a pulse voltage control signal and a base voltage control signal, which are applied to respective regulators 7 and 8. Since the signal for the average value of the welding voltage of an electric power source 6 is fed back from a detector 16 for welding voltage, the average value is controlled to a constant value determined by the set current. The wire feed speed is also controlled to the constant value determined by the set current value with a control circuit 21. When the set current value changes, the three factors; pulse voltage, base voltage and wire feed speed, change as well in follow up said change, whereby always adequate conditions are selected.