An electron beam device includes an electron gun section having an internal space kept at an ultrahigh vacuum level for generating a primary electron beam, a mirror section having an internal space kept at a vacuum level lower than that of the electron gun section for scanning a specimen with an electron probe of the primary electron beam generated in the electron gun section and focused on the specimen, a differential exhaust diaphragm for providing communication in internal space between the electron gun section and the mirror section and passing the primary electron beam, and a control section for controlling respective constituent elements in the electron beam device. A diaphragm mechanism having a plurality of different diaphragm aperture diameters is provided between a second anode and a first condenser lens.