To easily adjust an arc voltage setting value with an arc voltage setting device by inputting a difference between output signals of a voltage detector connected between output terminals of an arc working power source and output signals of an arc voltage setting device and connecting an analog element between output terminals of an arc working power source wherein a conducting quantity varies in proportion to the input.

A conducting quantity of a transistor 13 varies until output signals Vr of an arc voltage setting device 14 become equal to output signals Vf of a voltage detector 10. Therefore, when a setting value of the arc voltage setting device 14 is risen, a base current of the transistor 13 becomes small, the conducting quantity is reduced and an output current from a DC arc working power source 1 is lowered. Consequently, a voltage between output terminals Tm1 and Tm2 rises and an arc voltage rises based on an output voltage and current characteristic of the DC arc working power source 1. To the contrary, when the setting value of the arc voltage setting device is dropped, the arc voltage drops.