PURPOSE: To prevent destruction of an element due to surge voltage at the time of breaking current and to reduce the cost remarkably, by adding a surge voltage suppressing circuit in an arc welding power source equipment.

CONSTITUTION: A surge voltage suppressing circuit 8 is constituted by providing a branch path in which a diode and a capacitor 10 are connected in series between both ends of a DC reactor, and further connecting a charging circuit including a high resistance 11 that forms a discharging circuit, a DC power source 12 and a diode 13 in parallel to the condenser 10. When the surge voltage generated in a DC reactor 5 when welding current is cut off exceeds the charging voltage of charged condenser 10, the diode 9 conducts to form a by-pass of current, and the surge voltage is absorbed by the capacitor 10 by leaving fixed voltage. The voltage applied to a switching circuit 6 at this time is suppressed to the voltage that has fixed latitude to withstand the voltage of the transistor of the circuit 6 and to the voltage that allows reignition of the welding arc after inversion of current.