An electron optical system that yields a beam voltage of 100 kV and a beam edge resolution of 20 nm was developed for a variably shaped electron beam writing system, the EB-X2. In order to improve the beam edge resolution, the objective lens and main deflector were designed on the basis of the uniform field concept, and the optimum beam half-angle was determined by beam profile calculations. The optimized design provides a beam edge resolution of 20 nm for a 650-μm-square deflection field and a beam current of 250 nA. Given the high acceleration voltage, it is possible that the electron optical column could be too high to fit into a clean room. To shorten the height of the electron optical column, the lens configuration was carefully examined. The results show that the height of the column is a minimum when the first shaping aperture is placed in the principal plane of the illumination lens. This finding enabled us to reduce the height of the column to 880 mm. The electron optical column was constructed and the beam edge resolution was measured. The measured values agree well with the calculated ones, which confirms that the constructed column has the performance expected of the EB-X2 electron optical system.