To make it possible to process a work, regardless of a thick body or large body, by casting large energy an electron beam to the work even when the length between an vacuum tube type electron beam tube and the work is long.

An electron beam cast from an electron beam tube 3 (EB tube) is passed through a window 4 to the inside of a process chamber 5 and cast onto an irradiating object 2 like resist or ink on a work 1. The inside of the process chamber 5 has an atmosphere of gases, such as helium, a mixed gas of nitrogen and helium, neon, and the like with density lower than air (nitrogen). Since there is the gas with density lower than the air (nitrogen) in the process chamber 5, the attainable length of the electron beam from the electron beam tube is made long or its attainable range is made large.