To form a bag port in a sealed bag without producing cut wastes and perform an aseptic filling/packaging work.

A rolled product of band-like consecutive members 8 having a series of bags W0 with circumferential sealed and closed edges is unwound, fed into an aseptic chamber 3. A lower section (a cutting part 14) of an upper edge seal part Wa of either one surface film or both surface films in each of the bags W0 is cut to form a bag port and subsequently a boundary 16 between each of the bags is cut and the bags are separated into individual bags W having the circumferential edges sealed. The bag W is transmitted to a filling/packaging device 2, the bag ports are opened to fill some filled products in the bag, the bag ports are sealed and then the filled bags are discharged out of the aseptic chamber through a discharging part 23.