PURPOSE: To prevent terminal cracking of a welded joint by one side welding and to improve the quality of the joint by welding a tab to the end face in the terminal part of welding, and heating the tab beforehand while restraining the same with a restraining jig before the arc arrives at the terminal part.

CONSTITUTION: A welded joint 29 in one side welding of base materials 28 is subjected to sealing welding over about 1,000mm from the end face in a terminal part 30 of welding and is firmly welded with a tab 31 consisting of a mild steel material on the end face. The recess 33 of a restraining jig 32 is disposed onto the tab 31, and wedges 34 made of steel are fitted into the clearance between the tab 31 and the side wall of the recess 33, whereby the tab 31 is restrained from the arrow directions. The center of the tab 31 is heated to about 600W 800°C, and the arc welding of the joint 29 is started. The heating is stopped and while the tab 31 is so insulated of heat as to be kept at ≥500°C, the part 30 is welded. After the end of the welding, the part 30 is kept restrained by the tab 31 until the temp. of the deposited metal drops to about 400W500°C.