PURPOSE: To miniaturize the whole of an electron beam device such as an electron beam tester.

CONSTITUTION: A housing port 12a in which a slide plate 28a is housed is provided on an opening end part of a main chamber 11. A drawing-out electrode 10k and a sealing part sealing a main chamber opening are provided on mutually different positions on the slide plate 28a. The slide plate 28a is driven with an actuator 28p in a direction nearly orthogonal to the optical axis of an objective magnetic field lens 10h, so that either of the drawing-out electrode 10k or the sealing part can be located on the electron beam outlet part of the objective magnetic field lens 10h, and also the main chamber 11 opening can be sealed when the sealing part is located on the electron beam outlet part of the objective magnetic field lens 10h.