Provided are method for maintaining sterility and a simple and economical sterilization electron beam irradiating apparatus for maintaining sterility, which can prevent a target from being contaminated by germs during the entire irradiation treatment of an electron beam from the sending-in to the sending-out of the target, thereby to maintain the sterilized state satisfactory.A pre-pressure adjusting bath (20) and a post-pressure adjusting bath (30) are integrally jointed to the side face portion of an irradiation treatment bath (10), which is equipped with pressure reducing means for keeping a negative pressure state, and rotary carriers (11, 21 and 31) for transferring continuously containers to be irradiated are rotatively arranged in the individual baths. The irradiation treatment bath (10) is equipped with at least one electron beam irradiating means for irradiating the target with the electron beam. Clean air feeding means (50) is connected through a blower duct (51) to the side of the post-pressure adjusting bath (30), and an exhaustive system (52) is connected to the he side of the pre-pressure adjusting bath, thereby to adjust properly the pressure in the post-pressure adjusting bath (30) adjacent to the irradiation treating bath (10) and the pressure in the pre-pressure adjusting bath (20) adjacent to the irradiation treating bath (10).
