PURPOSE: To provide excellent close adhesiveness and heat-sealing strength to various bag bodies for packing food by introducing gas into a tubular film heat-sealed in the direction crossing the axial direction thereof and applying corona discharge treatment to said film while the inner surfaces of the film are held to a mutual non-contact state by said gas.

CONSTITUTION: A long tubular film 1 is successively heat-sealed in the direction crossing the running sealed parts 7 and becomes a heat-sealed tubular film. Gas such as air is blown in the heat-sealed long tubular film (bag-like long article) 1 from a hole 8 by an air filling apparatus 10 to form individual bag body formed parts 11 filled with air. In this state, the film is subjected to corona discharge treatment in such a state that the inner surfaces of the film are not brought into contact with each other. The bag-like continuous article 1' is squeezed by guide plates 22 to exclude air gradually and sent to a suspending and slacking part 23. Subsequently, opening scheduled parts are cut if necessary to obtain individual bag bodies 27.