The present invention relates to a migration of a file from a path denotative NAS server to an ID denotative NAS server. In a file management device according to one embodiment, a migration-use path denotative NAS access section obtains a file deposit location from the path denotative NAS server, selects a migration target file based on the deposit location, and sends a read request with the deposit location of the migration target file to the path denotative NAS server, so as to obtain the migration target file. A migration-use denotative NAS access section 44 generates a write request with the migration target file, sends it to the ID denotative NAS servers, and writes the file therein. In addition, the migration-use ID denotative NAS access section registers a GUID received from the ID denotative NAS servers in a file name/GUID management table, together with the file name of the migration target file.