PROBLEM TO BE SOLVED: To efficiently perform sterilization processing of a bag.SOLUTION: Plural bags (1) which are not sealed and to which a pouring mouth member (2) is attached respectively, are mutually separated, and the bags are filled in a cassette rack (6), and the cassette rack (6) is put into a sterilization chamber (7), and a sterilization step is performed once or plural times, in which the sterilization step comprises: a step for making the sterilization chamber (7) a vacuum state a step for introducing gas of hydrogen peroxide into the sterilization chamber (7) in the vacuum state a step for introducing asepsis air into the sterilization chamber (7) a step for discharging the hydrogen peroxide by making the sterilization chamber (7) the vacuum state and a step for introducing the asepsis air into the sterilization chamber (7).SELECTED DRAWING: Figure 2
