PURPOSE: To eliminate the irregularity in welding to be executed repeatedly by detecting an output state while supplying welding current with pulsating currents and maintaining the same in a prescribed state.

CONSTITUTION: The welding current from the start till completion of welding of the arc welding work for specific members is supplied continuously in the form of pulsating currents A1WAn obtd. by dividing said current with the arbitrary unit time segmented by fine time pulses as a unit for division. An intended pattern signal is formed from the state of voltages, pulsating frequencies and pulsating range. On the other hand, in the actual welding work, the currents A1WAn are kept supplied and during said supply, the voltages and pulsating frequencies are detected at all time, whereby the current pattern signal is formed. While the current pattern signal is compared successively with the intended pattern signal, the welding current A' is controlled.