PURPOSE: To prevent the occurrence of such a case that writing and reading on and from a floppy disk become impossible due to the hardware error of a file area management table (FAT) by providing two FATs having the same control information in the file system of the floppy disk.

CONSTITUTION: The file system 2 of a floppy disk controlling section 1 manages control information corresponding to all clusters on a floppy disk medium 6 in accordance with a directory 5 on the medium 6 and two file area management tables FAT A 3 and FAT B 4 in order to manage names and all information of files. Thus two FATs A 3 and B 4 having the same control information are provided. Therefore, even when a hardware error occurs in the FAT A 3, the file system 2 can make data reading and writing from and on the floppy disk by reading the FAT B 4.