There is provided an electron beam sterilizer, judging, in an electron beam irradiation zone, whether an electron beam amount to be irradiated to a resin bottle 2 is proper or improper. The sterilizer includes an electron beam irradiator 16 for irradiating the resin bottle 2 with an electron beam through an irradiation window 18 and a bottle conveyer 20 for conveying the resin bottle 2, and the resin bottle 2 conveyed in front of the irradiation window 18 is irradiated with the electron beam to thereby sterilize the bottle 2. A beam collector 46 is disposed in front of the irradiation window 18 so as to oppose thereto. The beam collector 46 is supported in an electrically insulated manner by an insulating member 48. When the electron beam irradiates the beam collector 46, an electric current flowing into the beam collector 46 is measured by an electric current measuring device 52. The measured electric current is compared with a predetermined reference value by a comparator 54, and a judging unit 56 judges whether an amount of the electron beam irradiated to the resin bottle 2 is proper or improper. In the judgement, when it is judged to be improper, the improper resin bottle 2 and other resin bottles 2 conveying before and after that resin bottle 2 are removed by a reject unit 24 in accordance with instructions from a command unit 58.
