PURPOSE: To obtain the welding zone of good quality even with an increased rate of deposition by making the relation with a filler material quantity per unit length of welding current and welding line as the specified conditions in case of welding a V shape butt bevelling in a upward posture.

CONSTITUTION: The defect of a defective fusion, etc. is caused due to excessive molten pool being made wen the rate of deposition exceeds 5.3g/min in case of welding a V shape butt bevelling in a upward posture. Now the relation between a welding current (Y) and the quantity of a filler material (X) per unit length of a welding line is made to satisfy the equation. However, X is taken as g/cm and Y as the figure by A. Even in the case of the rate of deposition exceeding the 5.3g/min considerably the welding zone having good penetration is obtd. with said method.