To surely and efficiently fill inert gas into a tray, in an electron beam irradiation device for storing a treated object in the tray, for filling the inert gas into the tray, and for irradiating an irradiated object in the tray with an electron beam.

The tray 7 storing the irradiated object W and closed with a sheet S is moved from an external tray table 6 outside an electron beam irradiation chamber 2 to an upper side of a tray table 3 inside the irradiation chamber 2, by a tray carrying-in device 5, the tray is brought down thereafter to the tray table 3 to be laid thereon, an opening and closing valve 31 provided in the tray table 3 is opened thereby pushedly by a pressing member 73 in a tray side, the inert gas is introduced into the tray 7 to be filled, and the tray 7 is moved together with the tray table 3 in an electron beam irradiation area. In addition thereto, the inert gas is filled also into the tray 7 which is under a stand-by condition in the an external tray table 6a.