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