PURPOSE: To keep the deaerated condition in a bag by pressing or cooling after heating by a method wherein a gap for ventilation is provided by 2 rows of temporarily sealed lines on the opposite side of an opening of a plastic bag of which one end is opened, and a non-welded part is provided on the temporarily sealed lines, and a non-welded part of the adjacent temporarily sealed line is provided at a location which apart from the other non-welded part.

CONSTITUTION: In a content putting process, a content 9 is inserted from an opening 3 of a plastic bag, and in a lateral welding process, the opening 3 is laterally welded. In a deaeration process, when the plastic bag is pressed from a laterally welded part 14 to the main body, a first temporarily sealed line 4, and second temporarily sealed line 5 orderly, air in the plastic bag is discharged from a non-welded part 6, and a back flow of the air does not generate. Then, in a complete welding process, the first temporarily sealed line 4 and second temporarily sealed line 5 are completely welded to obtain a deaeration packaged bag. Therefore, the deaeration in the bag can be held by simply pressing or cooling after heating, without providing deaerating and welding devices, and using the welding device right after a deaeration in order to seal the bag opening.