1 2f and a total of four in one cycle f then the time t1 of the pause straight line b of the welding current waveforms and the time t2 of the pause straight line b1 are set at t1 t2 and the time t3 of the drop pause straight line d is set at n times of 1 or more number including decimal point of n 1 or more of the set duration of t12 t2 therefore each duration of t1 t2 t3 of the pause straight line b and drop pause straight line d can be set by tuning moreover the rising current set value s1 can be set and the drop rate dr rate from the rising current set value s1 to the current drop set value s2 can be set at this time the drop rate is set and adjusted so that the duration of t11 from start of the first rising straight line a till end of the first pause straight line b in the welding current waveform and the duration of t12 from start of the first drop straight line c till end of the second pause straight line b1 at the end side of the first pause straight line b may be in the relation of t12 t11 u00b1 t11 u00d7 0 to.