PURPOSE: To enable a high drawing accuracy to be maintained by measuring an electron beam diameter on a drawing material with a specified reduction rate of an electronic optical system and then adjusting the electronic optical system based on this measured value.

CONSTITUTION: With excitation of a reduction lens being 0, a beam size on a material 4 is set to a specified reduction ratio and an objective lens power supply 9 is controlled, thus enabling automatic focusing operation to be made by the objective lens 3. After the focusing is completed, deflection signal for measuring a beam size is supplied from a calculator 12 to a deflector 5 through an amplifier 13 and then the beam is scanned straightly across a mark M. The generated reflection electron is detected by a detection element 6 and is stored in a waveform memory 11 after amplification by an amplifier 10. The calculator 12 sets the width of a half-life value of a wave- height value of the waveform to a beam diameter, obtains the size of an electron gun cross over from the reduction rate of the optical system, controls a power supply 8, and then sets the strength of the reduction lens so that the beam diameter on the material 4 becomes a desired size. After the beam diameter is adjusted, a highly accurate pattern can be drawn by supplying deflection signal to the deflector 5.