Upon integration of a file system, user identifier recorded in a storage as management data is translated. A file server connected to a storage storing the data of a file system therein has a file system operation unit for managing the file system, a file server operation unit for receiving the access request to the file, and a user identifier translation unit for carrying out translation between first user identifier, which is used by the client and second user identifier, which is recorded in the storage as management data of the file system. Receiving the access request to the file from the client, the user identifier translation unit translates the second user identifier included in the management data of the file that is an access target of the access request into the first user identifier, and the file server operation unit transmits the management data to the client.