PURPOSE: To control easily a log of information, by providing a control label indicating the validity, invalidity and sleep on each information area unit, detecting its control label at the time of registration and deletion of a file, and opening from the oldest one of the sleep area if the registration request is more than the number of invalid areas.

CONSTITUTION: The entry constituting items controlled by a control table registration block 15 consist of a flag 1 for indicating the validity, invalidity and sleep of a file, a file name 2, year, month, day and time 3 and a comment 4 of the file. When recording information is controlled by this entry item, an access command of the file is sent to an interface control block 12 from a CPU 11, the file name 2 is sent to a file name retrieving block 13, and the flag 1 on a registering block 15 is retrieved by the block 13. In this way, the flag 1 is detected at the time of registration and deletion of information, and when the registration request is more than the number of invalid areas, the opening is executed from the oldest one of the sleep area, and a log of the information is controlled easily.