PURPOSE: To constantly enable smooth opening without interfering air stream for opening on a base where bags are stacked by a method wherein a fixing piece is extended on each of right and left upper rims of a sealing piece and scores are provided between the fixing piece and the upper rims of the sealing piece.

CONSTITUTION: Side rims 5 of a surface film 1 and a rear film 2 are fused to form a bag body while a sealing piece 3 is extended from the upper rim of the rear film 2 and fixing pieces 7, 8 are connected via scores 9, 10 to the right and left upper rims of the film 2 to form a wrapping bag. After the wrapping bags are stacked on a wrapping base 30 and the stacked fixing pieces 7, 8 are fixed by two clips 14, air stream is blown against the upper rim 4 from a nozzle 12 provided on the center line of the bag so that the upper rim 4 is made float to be opened and a product 16 is mechanically inserted from the opening. After insertion the air stream is stopped, the scores 9 and 10 are cut away and the bag is moved from the wrapping base to a sealing base with the fixing pieces 7, 8 left so that the sealing piece is folded toward the upper rim of the bag and an adhesive tape 13 is adhered on a joint of the sealing piece 3 and the upper rim film to have them adhered to each other.