PURPOSE: To realize the simple correction of the data on a ROM file by comparing this data with the data on the ROM file stored in a buffer RAM and storing the data, the address and the ID of a different part of both data into the RAM as the correction information.

CONSTITUTION: It is first checked whether the correction information can be stored or not in a RAM 4 before the information is actually stored. In other words, a counter K for corrected data is initialized together with an additional character (n) for work. Then the comparing step for data between a buffer RAM 1 and a ROM file 6 is repeated together with the addition step of the counter K carried out when data are different by the frequency equal to the number C of data. Thus the number of corrected data is set to the counter K. Then a counter L for correction information on an empty ID of the RAM 4 and the character (n) are initialized repetitively until the reference given to the correction information. Thus the storage enable number L of the correction information is set.