PURPOSE: To make possible the prevention of seizure by providing a regulating circuit for a specific output current and changing over the output current of a welding machine when arc voltage becomes lower than reference voltage in the case of performing arc welding by the use of a consumable electrode.

CONSTITUTION: A comparator 8 comparing arc voltage and reference voltage, as well as the normally open contacts 9 of a relay 10 actuating only during the generation of the arc and a relay on the output side of the comparator are provided. The make and break contacts of this relay are provided to a regulating circuit 18 for the output current of a welding machine 16. If the regulating circuit 18 of the welding machine 16. If the regulating circuit 18 of the welding machine is operated, the arc is generated between a consumable electrode 5 and the welding works 6. If the reference voltage is set lower than the seizure threshold voltage, the comparator operates upon rising of the voltage at above the arc voltage during welding, causing the relay to go on and a steady signal circuit 19 to go off. On the other hand, an emergency signal circuit 20 goes on to lower the output voltage; therefore, the rate of melting of the consumable electrode decreases and the seizure phenomenon does not occur.