PURPOSE: To check the consumption state of an electrode and to obviate welding with an inadequate electrode in the stage of starting welding, etc. by comparing the arc voltage when a specified current is flowed to a specified arc length and the voltage of a reference signal circuit.

CONSTITUTION: A driving circuit 7 runs motor 6 upon starting of welding, and a torch 1 moves downward. An arc length setting circuit 8 detects the contact of an electrode 2 with a base material 4 and pulls the torch 1 by a specified distance. The initial current by an initial current setter 9 flows and the arc voltage and the output of a reference signal circuit 12 are compared in a comparator 13. If said output is of the value having no problems in welding, a judging circuit 14 emits a command to a current change-over circuit 11 which changes over the setter 9 to a welding current setter 10 thereby progressing the welding operation. If the output is inadequate, the setter 9 is interrupted and the cutting operation by melting is stopped.