To enable the welding of large current in any posture, to enable the shallow penetrated welding of the large current and to repeatedly execute the short circuit and the arc development which can weld a thin plate at high speed, by making the higher output voltage in an electric source for welding at the time of developing the short circuit than that at the time of developing the arc.

It is desirable that the output voltage in the electric source for welding during the interval from the starting time point of the short circuit to a fixed time after completing the short circuit is made higher than the output voltage in the case of being the other time, or the output voltage in the electric source for welding during the interval from a fixed time after starting the short circuit to a fixed time after completing the short circuit, is made higher than the output voltage in the case of being the other time. Further, it is desirable that the repeating frequency for developing the arc and developing the short circuit is detected and according to the difference between the repeating frequency and the reference frequency, the output voltage is decided in the term which is made high output voltage of the electric source for welding, or the repeating frequency for developing the arc and developing the short circuit is detected and according to the difference between the repeating frequency and the reference frequency, the fixed term is decided.