To attain appropriate archive management by using a random accessible device.

An archive management part 1B reads a file stored in an on-line volume 5A in timing decided for every file type, and stores it in a predetermined volume of archive volumes 5B1 and 5B2. The storage period of the file data is designated, and each volume 5B1 and 5B2 is also set with the storage period. The file data are stored in the volume having the storage period matched with the storage period of the file data. Each volume 5B1 and 5B2 is set in a random accessible device such as a hard disk. A region where data have been written in each volume 5B1 and 5B2 is managed as a write inhibition region by a pointer P. Thus, each volume 5B1 and 5B2 can be used as, so called, a WORM device.