PURPOSE: To prevent generation of drawing at the end part of welding and hole formation in the course of welding, by placing a welding stabilizing material between a fixing jig of a material to be welded and a material to be welded, simultaneously welding the welding stabilizing material, too, and thereafter, removing it.

CONSTITUTION: Materials to be welded 4a, 4b of two dead thin plates are placed at a prescribed position by butting the end parts, subsequently, dummy plate materials 6a, 6b are disposed, and in the end, these materials are clamped and fixed by fixing jigs 3a, 3b. A butt part 5 of the materials to be welded 4a, 4b is welded by moving a welding torch from one dummy plate material 6a to the other dummy plate material 6b, on the butt part 5. In that case, a welding stabilizing material 8 existing in the lower side of the butt part 5 is also welded simultaneously to the lower face of the materials to be welded 4a, 4b, in the butt part 5. After welding is finished, the welding stabilizing material 8 which is welded jointly is removed, and the same state as only the materials to be welded 4a, 4b are butt-welded is obtained.