To provide a butt welding method for thin steel sheets by which a sound weld zone is obtained in sheet join welding.

When a bevel line of a butt joint, in thin steel sheets such as cold rolled steel sheets, obtained by butting both the edge faces of the rear end in the preceding sheet and the front end in the posterior sheet is melted and welded by TIG welding or the like while performing back shielding, the bevel line of the butt joint is welded from the side wall of a groove provided at a backing strip for back shielding in the range where 0.7×t is satisfied to the space side of the groove and 1.4×t is satisfied to the base metal side of the backing strip in accordance with the sheet thickness (mm) of the thinner one of the preceding steel and the posterior sheet.