To stably realize the short circuit transfer type arc welding.

In the short circuit transfer type arc welding which is conducted while repeating short circuiting and arcing with using a welding power source of roughly a constant voltage characteristics to adjust a time constant of a output current change by a electronic reactor circuit, an inductance value of the electronic reactor circuit of the welding power source is set to an inductance value lower than one in other times for the time of short circuiting or for the interval from a short circuit start time up to a fixed time after short circuiting completion time or from after a fixed time after a short circuiting start time up to after a fixed time after a short circuiting completion time.