At a conveying path 10 for continuously carrying a sheet material 1, an electron beam irradiation means 20 is arranged in opposition to at least one surface of the sheet material 1, and at least one surface of the sheet material 1 is sterilized using such an electron beam. The conveying path 10 takes shape of a hollow box surrounding the sheet material, and has an electron beam irradiation area 11 at a part of this area, while keeping a reduced-pressure state ranging from 10 to 80,000 Pa using a pressure reduction means 16. Further, the electron beam irradiation area 11 where the electron beam irradiation means 20 is arranged at least one sub area 12 at each of adjacent hollow box-shaped conveying path 10 at carry-in side and carry-out side of the sheet material, providing the pressure reduction means 16 for depressurizing the sub area 12.
