To provide an electron beam irradiator which equally irradiates only the entire surface of granular objects such as grain and plant seeds with a low-energy electron beam, completely sterilizes the entire surface of the granular objects, enables high-speed sterilizing treatment, has high reliability and does not require a large setting space and a method for sterilizing the granular objects by using the irradiator.

In this invention, the electron beam irradiator which can irradiate the entire surface of the granular objects with a low-energy electron beam without rotating the granular objects by allowing the low-energy electron beam to run on an orbit shaped like a cone from an annular cathode of a small diameter toward an annular electron transmission window of a large diameter and providing a means for passing the low-energy electron beam through the back or the side of the granular objects existing in an object passage formed so as to surround the annular electron beam transmission window and the method for sterilization using the irradiator are provided. Moreover, reasonable electron density is realized because the irradiator has a structure which has a small cathode, the electron transmission window of a large diameter and the object passage of a larger diameter and the throughput capacity can be heightened extremely because the irradiator can be cooled properly.