In a folding completion body of an airbag, the airbag includes: an airbag body configured to be stored on an upper edge of a window on an inboard side of a vehicle; and a plurality of mounting pieces which extend from an upper edge of the airbag body and mount the airbag body to the upper edge of the window, the lower edge of the airbag body in a flatly deployed state is folded to be brought close to the upper edge so as to form a folded body; a folding-collapse preventing member is assembled to the folded body; and the mounting piece with the lug is folded and superimposed to the upper edge of the airbag body in the folded body, and the lug is interposed between the folding-collapse preventing member and a surface of the folded body so as to be fixed to the folded body.