PURPOSE: To provide an electron beam irradiator in which the window foil is protected against scratch or breakage due to an object to be processed.

CONSTITUTION: An irradiation window part comprises a metal window foil 32 and a window frame structure 34. The window frame structure 34 comprises a window frame 44 and a retainer 54 for retaining the window foil 32 to the window frame 44. The retainer 54 has a large rectangular opening across which a large number of wires 58 are stretched. The wires 8 are inclining by a predetermined angle θ against the carrying direction X of an object and stretched linearly. A metal having high melting point, e.g. molybdenum or tungsten, or a ceramic is employed as the material of the wire 58.