PURPOSE: To reduce the size of welding equipment for tacking and to maintain high accuracy of an assembled automobile body by forming a nugget with a smaller diameter than that of the nugget of a work by the additional spot welding.

CONSTITUTION: A cylinder 34 is pressed by air with panel parts P to be welded between and a copper plate of a feeding terminal 32 is pressed and held by the electrode tip of a gun 40 for feeding. The small nugget to the extent that the tack-welding strength is obtained by a welding current supplied through a secondary cable 33 is formed to a weld zone and the respective panel parts P are tacked. Then, when welding places are moved in order and when the predetermined necessary number of spots of the spot welding is completed, the welding work is stopped and respective fixtures 21 and 22, etc., to hold the respective panel parts P in-between are released. The tack-welded automobile body is mounted on a shuttle bar 17 and moved to an additional spotting stage and the additional spot welding is performed to form the automobile body with the sufficient assembled strength.