An electron beam system wherein a shot noise of an electron beam can be reduced and a beam current can be made higher, and further a shaped beam is formed by a two-stage lenses so as to allow for an operation with high stability. In this electron beam system, an electron beam emitted from an electron gun is irradiated onto a sample and secondary electrons emanated from the sample are detected. The electron gun is a thermionic emission type and designed to operate in a space charge limited condition. A shaping aperture and a NA aperture are arranged in front locations of the electron gun. An image of the shaping aperture formed by an electron beam emitted from the thermionic emission electron gun is focused onto a surface of the sample through the two-stage lenses.