An object of remote copy can be specified in units of a file or a directory more detailed than in units of a volume. If a host computer issues a write request of a file to NASa, NASa references a source NAS of remote copy and a source directory of remote copy at each entry on a copy file table and determines whether the file to be written is an object of remote copy; if it is determined to be an object of remote copy, the file to be written is remotely copied to a target directory of remote copy of a target NAS thereof.