To ensure the maintenance of the devices, by vacuuming the inside of a pair of chambers, free to be opened and closed, which incorporate transfer means, by filling nitrogen gas into the vacuum chambers, and by closing and sealing a bag mouth.

A nitrogen sealing machine is equipped with a buffer between a bag-folding part for folding a bag mouth and a nitrogen-sealing part for sealing in a nitrogen gas in this condition and sealing the bag mouth. In the nitrogen-sealing part, by operating a pair of chambers 3 and 4 by means of air cylinders, the bag mouth put in a box sent by a conveyor is hermetically sealed by the face-packing of one of the chambers, 3 and 4, and the projecting edge of the other. The inside of each chamber is vacuumized, and then nitrogen gas is sealed in it. Also, the four air cylinders 43 are operated, and then the bag mouth is sealed while a seal bar is kept pressed, and, thus, the bag is neatly shaped and sealed in a normal, undeformed state.