Data storing system using network

An agent program installed in a terminal device is used to upload data, which are to be stored, to a data storage device via a first network (N). Data uploaded to a first data storage unit are stored therein as they are. On the other hand, data uploaded to a second data storage unit are transferred, by the function of a data transferring unit, to any of external storage sites (-) via a second network (N), and management information, which includes the URL of the storage site that is the transfer destination, is stored into an IC card. When the data stored in the data storage unit are required, the management information in the IC card is given to the data transferring unit and the relevant data are forwarded from the storage site that was the transfer destination to the data storage unit and then downloaded to the terminal device. The limit of the storage capacity can thereby be overcome and damages due to viruses can be suppressed.