A data intermediate server 300 comprises the functions of reading data stored in storage servers ST1 through ST3 and sending the data to a media server 600 according to backup commands received from a backup control device 400 over a local area network LAN4. The data intermediate server 300 and the storage servers ST1 through ST3 are connected by channels that do not permit Internet protocol traffic but only data targeted for backup and control data assigned thereto. As a result, client data stored on the storage servers can be properly backed up while preventing data from being improperly retrieved or leaked.