PURPOSE: To recover management information on a file when abnormality occurs.

CONSTITUTION: Block management information is composed of the number of blocks, which corresponds to the file blocks in a data part storing the file by one to one. The respective blocks consist of use file identification name storage areas B1 storing identification information on the file and next address display areas B2 storing next address information showing the link destination of the blocks. A directory consists of HEAD storing head block addresses for the respective files in block management information and TAIL storing the number of blocks having the same file identification information and final addresses for the respective files. Furthermore, lowest number free area management information storing the head block address of the free area of block management information is provided. Even if link information linking respective blocks is lacked, the blocks having the same file identification information are linked in an ascending order so as to reproduce block management information.