There is provided a file management method of a hierarchy management file system capable of preventing an access performance from dropping when a user accesses to a file. According to the method, a server creates file systems in high-speed and low-speed volumes and a file-sharing server virtually integrates those file systems into one system as a pseudo file system. Then, the server moves a file to be moved to the file system created in the low-speed volume in advance, not when an access is made to the file. When a user accesses to the file after that, the user directly accesses to destination without requiring to copy the file, so that the accessing performance may be prevented from dropping.