To easily and quickly attain saving and restoration of a volume by saving residual assets by restoring a VTOC, without using backup data.

Whether the damage of a VTOC is caused by a hardware error or a software error is recognized by a recognition processing part 51, and when it is caused by the hardware error, a file management block and a dead management block remaining in the VTOC are referred to, and information in the dead management block is arranged, so that a file storage area can be matched with a dead area in the VTOC, and after this matching processing is completed or after it is recognized that the damage of the VTOC is caused by the software error, a data area (dead area) is retrieved, and information related with the residual file is detected by a re-constitution processing part 53, and a file management block for managing the extent of the residual file is prepared based on the information, and registered in the VTOC.