Nitrogen oxide generated in an irradiation chamber 30 by electron beam irradiation is suppressed from being changed to nitric acid.An irradiation surface (irradiation window 29a to which a window foil 29b is attached) of an electron beam irradiation device 28 is directed toward a vessel 2 conveyed by a vessel conveying device 24 to thereby irradiate the vessel 2 with the electron beam to sterilize the vessel, an irradiation chamber 30 is provided so as to surround the irradiation surface of the electron beam irradiation device 28 and the vessel 2 subjected to the irradiation, a discharge chamber 32 is provided on an outlet side of the irradiation chamber 30, and dry-air supply means 80 for supplying a dried aseptic air is connected to the irradiation chamber 30. By removing moisture within the irradiation chamber 30 which is irradiated with the electron beam, the changing of the nitrogen oxide to the nitric acid is suppressed to thereby prevent metal portions from corroding.
