In a sterilization mode, plastic containers 2 fed by an article feeder 20 which is housed in a shield chamber 10 are sterilized by being irradiated with an electron beam that is radiated from an irradiation window 18 of an electron beam irradiation unit 34 which is coupled to an opening 32a of the shield chamber 10. In a maintenance mode, an adjustment irradiation box 60 is detachably mounted on the electron beam irradiation unit 34 in covering relation to the irradiation window 18 of the electron beam irradiation unit 34. The adjustment irradiation box 60 houses therein an electron beam receiver 66 for receiving the electron beam radiated from the irradiation window 18, a cooling mechanism 70 for cooling the electron beam receiver 66, and an exhaust mechanism 72 for discharging an atmosphere in the adjustment irradiation box 60. Maintenance work can be carried out on the electron beam irradiation unit 34 after the electron beam irradiation unit 34 is disconnected from the shield chamber 10.
