unnecessary and data conversion software for fracturing is used as tools a to c fig2 is a flowchart for describing a pattern data processing method according to the present embodiment it is to be noted that steps s 0 to s 2 before step s 3 are the same as those in fig5 of the first embodiment so that its explanation is omitted in the following as shown in fig2 a difference between the present embodiment and the first embodiment see fig6 is that fracturing is performed in steps s 4 and s 16 instead of opc fracturing is a process which converts a format of pattern data into a format of data for an electron beam exposure system used for drawing a mask pattern on an exposure mask in the present embodiment as the pattern data the design data on the mask pattern before or after the opc is performed is employed then similar to the first embodiment the process in steps s 1 to s 5 and s 16 are performed on the pattern data the format of the data includes gds oasis mebes jeol52 hl 700 hl 800 hl 7000 vsb11 and bef advantest among these data on two different formats respectively become input data and output data in the fracturing then as a result of the processes.