In order to access a distributed file system (DFS) of the present invention using a conventional protocol such as the one for an NFS or a CIFS without making a modification on a client side, a gateway unit for receiving a conventional protocol and performing processing in conformity the protocol is provided for a DFS server. The gateway unit emulates a directory structure in a file system such as the NFS or CIFS. When the DFS is a write-once read-many file system, update processing is converted into processing for creating a new generation file, and reference processing is converted into access to a latest generation file in a generation-managed file group. The gateway unit then accesses a DFS file via a DFS processing unit.