An ultra-miniaturized electron optical microcolumn is provided. The electron optical microcolumn includes an electron-emitting source emitting electrons using a field emission principle, an extraction electrode causing the emission of electrons from the electron-emitting source, a focusing electrode to which voltage is flexibly applied in response to a working distance to a target for regulating a focusing force of electron beams emitted from the electron-emitting source, an acceleration electrode accelerating electrons emitted by the extraction electrode, a limit electrode regulating an amount and a size of electron beams using electrons accelerated by the acceleration electrode, and a deflector deflecting electron beams towards the target.