To provide an electron beam generator that can generate a stable electron beam as the current accompanying the production of larger current electron gun, in an electron beam irradiator.

The beam passage hole diameter of an accelerating electrode 2 in the electron beam generator is set at 40 mm to 300 mm inclusive, whereby the operation of the electron beam generator is stabilized by eliminating collisions of beam electrons with the accelerating electrode 2, even if the instability of a potential associated with the electric discharge near the electron gun 7.