Based on dimensional analysis, a configuration of a microlens system for focusing an electron beam can be obtained by the dimensional scaling down from a conventional lens. An electrostatic microlens system consisting of two planar microsize apertures has been investigated. For this microlens, the spherical and chromatical aberrations, the astigmatism due to elliptic distortion, and the displacement due to misalignment have been calculated in detail. The resolution has been derived by a general formula, and thus has been evaluated numerically. The computational results have shown that the miniaturized microlens system proposed in the present article possesses remarkably small aberrations and ultrahigh resolution in the low voltage operation, and will be likely applicable for some practical uses.