PURPOSE: To determine a constant area of a weld position in the stage of attaching a bar code card by welding to a prescribed work by forming preliminarily an embossed part to a part of the bar code card and welding the card at said part to the prescribed work.

CONSTITUTION: An embossed part 5 is preliminarily worked by pressing to the corner part except the region to be inscribed with bar codes of a bar code card 2. Said card 2 is handled by a manipulator or the like so as to be set in the required position of a body Bo which is a work. The card 2 and the panel on the body Bo side are then pressed and welded by the electrodes of a projection welding machine.