PURPOSE: To enable drawing time to be reduced by memorizing distortion coefficients on a plurality of grid points which are used for correcting distortion of patterns within each divided section of a drawing region at each same address of a plurality of memories.

CONSTITUTION: A specified amount of drawing data is stored in a drawing data memory 8 from a magnetic disk according to a command of a control device 7 previously. Before drawing a pattern, a deflection distortion correction coefficient at each grid point of fields which are divided in grid shape obtained from mark detection and interpolation method is stored in memories 9A-9C. In this case, the same deflection distortion correction coefficient is stored at a negative address with one X address for the memory 9B for an address of the memory 9A and is stored at a negative address with one X address and one Y address for the memory 9C, thus enabling needed plurality of deflection distortion correction coefficients to be called from each memory by performing addressing once for one pattern to be drawn. Therefore, time required for recalling in entire drawing can be reduced.