Atmosphere in a sterilization box 18 is prevented from entering into a filler chamber 44 side, and also, atmosphere on the filler side is prevented from flowing on the sterilization box 18 side. An intermediate chamber 40 is disposed between the sterilization box 18 for performing sterilization by electron beam irradiation to a vessel 2 and the chamber 44 in which a filler 42 is disposed for filling the sterilized vessel 2 with inner content. A pressure in the intermediate chamber 40 is controlled, by a pressure control device, so as to be higher than a pressure in the sterilization box 18 and higher than a pressure in the chamber 44 provided with the filler 42. Since the pressure in the intermediate chamber 40 is highest, atmosphere in the upstream-side sterilization box 18 is prevented from flowing in the filler 42 side and atmosphere in the chamber 44 for the filler 42 is also prevented from flowing in the sterilization box 18 side.