PURPOSE: To make unnecessary a file altering processing such as leaving a copy history after a copy program execution when a file preparing date and a time are reset to the specific date and time by providing a function, which rewrites the copied file preparing date and time as soon as the file is copied.

CONSTITUTION: A file read processing part 5 reads the file from a copy source disk whose file copy command is designated to a memory. At such a time, when a date/time parameter is set by the file copy command, the date and time stored into a date/time parameter storing area 4 are written to a file data/time setting part in the memory by a date/time altering processing part 6. Next, a file write processing part 7 writes the file, whose date and time are altered, on the memory to a copy destination disk whose file copy command is designated. Thus when the file preparing date and time are reset, the processing to newly alter the file after the execution of the copy program is made unnecessary.