Examples include a photoelectric film that emits electrons by irradiation of an excitation light, an extraction electrode for extracting emitted electrons, and a differential exhaust diaphragm through which extracted electrons pass. A control unit controls an electric field formed in relation to the extraction electrode to make the extracted electrons pass through the differential exhaust diaphragm both in a first case in which the excitation light is irradiated to a first position of the photoelectric film, and in a second case in which the excitation light is irradiated to a second position different from the first position of the photoelectric film.

Provided is an electron gun chamber for a scanning electron microscope with (a) an electron source chamber; (b) an intermediate room; (c) an air lock valve installation part; (d) exhaust holes for a preliminary vacuum exhaust pump; and (e) an opening and closing means.