PURPOSE: To prepare the frequency distribution of various combinations with the conditions of various combinations and to attain rapid processing by providing this frequency distribution preparing circuit with a means for preparing frequency distribution and a means for outputting a frequency distribution preparing request to the succeeding FPGA block to release a current block.

CONSTITUTION: A CPU 1 loads data necessary for the preparation of frequency distribution from an auxiliary storage device 7 to a list memory 3. Then the CPU 1 clears the contents of a frequency distribution memory 4, sets up plural optional forming conditions in a mask memory 5, reads out logical circuit connecting information for preparing necessary frequency distribution from a program memory 2, and loads the information to respective FPGA blocks 11 to 14. Since the CPU 1 holds plural logical circuit connecting information, the frequency distribution of various combinations can rapidly be prepared by reloading these information on the CPU 1 during the operation of the system without changing hardware. Thus the frequency distribution of various combinations with the preparing conditions of various combinations can be prepared.