PURPOSE: To hold the data required for restoring in-file record management table (FAT) areas even when data destruction occurs in an FAT area by adding data for restoring FAT areas to the leading edge of a data record.

CONSTITUTION: When a record R6 is further written in a file A, the record R6 is written in the record storing area 14 of the data area corresponding to a FAT number '9' and the '9' is added as the in-FAT relative record information 12 of the record R5 which is the last record before writing the record R6. In addition, 'FF' is added as the in-FAT relative record information 12 of the record R6. Moreover, the '9' which is the in-FAT relative record information 12 of the record R5 is stored in the in-FAT relative record information storing area 13 of the record storing area 14 of the record R5. Therefore, even when the FAT area is destroyed, the data in the FAT area can be restored automatically by referring to the FAT data which are the pointers indicating next records at the leading edge of each record.