An electron beam apparatus is provided in which a sample is scanned with a
plurality of primary electron beams respectively emitted from a plurality
of electron guns. Each of the electron guns comprises a mechanism for
adjusting a relative position between a cathode and anode. The adjusting
mechanism of each of the electron guns comprises an insulator for
supporting the cathode and a plurality of piezo elements for supporting
the insulator. The piezo element varies its length in response to a
voltage applied thereto. Therefore, the position of the cathode is
adjustable relative to the anode position, by controlling voltages
applied to the piezo elements.