To provide an electron acceleration method facilitating maintenance of an electron beam device, and increasing the degree of vacuum in a vacuum chamber without operating a vacuum pump for continuous exhaust.

This electron acceleration method is structured such that an electron beam emission window 24 is airtightly brazed to a vacuum chamber 46 in a place controlled into a clean air environment; the vacuum chamber 46 sustainably keeping vacuum without operating the vacuum pump for continuous exhaust is arranged by welding or bonding and connecting to be sealed; electrons are generated by an electron generator 31 positioned within the vacuum chamber; the electron generator is surrounded by a housing 30; the housing is formed with an opening between the electron generator and the electron beam emission window for allowing electrons to be accelerated from the electron generator 31 to the outside of the electron beam emission window 24 in an electron beam when a voltage is applied between the housing and the electron beam emission window 24; molecules in the vacuum chamber is ionized; and the ionized molecules in the vacuum chamber are captured to increase the degree of vacuum in the vacuum chamber.