PURPOSE: To get a favorable resist pattern by changing the focus distance according to the desired pattern line width so as to do exposure.

CONSTITUTION: This is equipped with an irradiation control means 6, which optimizes focal length for every desired pattern size when exposing the pattern below the maximum shot side. And when exposing the pattern below the maximum shot size, it is exposed at a time by the charged particle beam having the desired line width of a pattern 3a, but it is exposed at the focal length being optimum for every desired line width, so the beam edge width of the entering charged particle beam becomes the minimum width for every desired line width. Hereby, good desired resist pattern can be gotten.