A welding facility includes a main welding line for manufacturing an assembly of frame members, and a sub-welding line for manufacturing an assembly of panel members, the sub-welding line merging with the main welding line. The main welding line is comprised of a plurality of welding stages provided with a welding robot, the sub-welding line is provided at the end with a transfer mechanism for transferring the panel member assembly to the desired welding stage, and the merging parts are changeable according to the type of product to be welded. The facility permits a plurality of vehicle bodies having different vehicle types to be manufactured using the same manufacturing line.