PURPOSE: To make welding having good appearance traces of welding by butting a material to be welded in which a filler metal part is formed at butted part and a material to be welded in which a groove part is formed at butted part and melting and filling the filler metal part in the groove part.

CONSTITUTION: In a pair of material to be welded 1 provided ribs 6 having J- shaped sectional form extending in longitudinal direction of outer surface in a body at intervals, rib forming sections 7 having thickness a half that of the ribs 6 is formed on both sides of each material 1 to be welded. A filler metal part 2 and a projected rib 4 are provided in one of opposing rib forming sections 7 and a groove part 3 and a recessed groove 5 are provided in another rib forming section. Materials to be welded 1 are tacked by fitting the recessed rib 4 in the projected groove 5, and the filler metal part 2 is welded and penetrated into the groove part and filled. Thus, the weld zone becomes the same shape with the rib 6. As the sectional form of the material to be welded 1 is J-shaped, the weld zone is not positioned at the center of the product, and does not hinder attaching of a name plate.