Abstract: An electron beam exposure system of a variable shaped electron beam type in which an input pattern of any geometrical shape is decomposed into rectangular patterns of a given size, whereby the pattern is exposed by an electron beam having a cross-section corresponding to the decomposed rectangular pattern. Data for the input pattern is compared with data for the rectangular cross-sectional pattern of the electron beam in a comparator. When the comparison results is that the input pattern should be decomposed into rectangular patterns, the former is decomposed into two sub-patterns, one of which is outputted while the other again undergoes the comparison with the rectangular pattern parameters. The processing of decomposition can be executed at a very high speed in a pipelined system which includes a plurality of processing stages of similar arrangement.