the surface of the reticle 2 is illuminated by an electron beam u201c illumination beam u201d passing through an illumination optical system not shown but understood as being situated axially upstream of the reticle the beam downstream of the reticle 2 is termed a u201c patterned u201d beam or u201c imaging u201d beam the reticle side lens 4 and wafer side lens 5 collectively form an image on the substrate of the pattern portion on the reticle 2 illuminated by the illumination beam the deflector 7 functions to deflect the patterned beam as required for forming respective images on the substrate 3 of reticle subfields that are displaced laterally from the optical axis hence the images on the substrate 3 similarly are displaced laterally taking into account the demagnification factor the dynamic focus coil 8 and stigmator 9 are used for correcting field curvature and astigmatism respectively accompanying beam deflection in conventional electron beam microlithography apparatus the dynamic focus coil 8 is maintained in a constant operational state as each shot is being exposed i e during exposure of a subfield in contrast in this embodiment the dynamic focus coil 8 is energized in a controlled manner to make corrections to the focal point as the exposure is being made thus the dynamic focus coil 8 has the function of micro adjusting the focal point at high speed during individual exposures normally the time required for an exposure of a subfield is about 0 1 u03bcsec during which time a change of approximately 25 u03bcm in the focal point easily can be accomplished by the dynamic focus coil 8 with the exception of the manner in which the dynamic focus coil 8 is operated in this apparatus embodiment as described above.