An irradiation electron beam emitted from an electron gun is deflected by an energy filter, and passes through a first projective lens and an objective lens, and then irradiated onto a sample to produce secondary electrons. The secondary electron beam accelerated by a negative voltage applied to the sample passes through the objective lens and the first projective lens, and deflected by the energy filter to be energy dispersed. Only the secondary electrons having a specified energy pass through energy selecting aperture, and further pass through a second projective lens to form a projected image of the secondary electrons on an imager. Such an electron-optical system may be used for dimension evaluation or inspection of semiconductor substrates.