PURPOSE: To save a time width (pulse width) required for data write by comparing a data with the content of a corresponding address of an EPROM after the data is set and skipping the write when they are identical and allowing the step to be moved to the next address.

CONSTITUTION: In an erasable and programmable ROM (EPROM), when a data is written to all addresses of the EPROM, a write data is checked and when the data is identical to a data of corresponding address not in use, the address is transferred to the next address. In such constitution, after data set the data is the same information as the non-operating state of the EPROM, e.g., "FF" (all digits are logical "1" in binary number), and when the data is coincident with it through comparison, the step moves to the next address set without being subject to the write signal supply as it is. Since the length of the program data given to the EPROM is short in this system and the next addressing is conducted for rhe non-use part without being restricted by the write pulse width, the time is reduced by the share.