A user device uses, instead of agreement information, only second session information contained in the agreement information, to generate an electronic signature for information containing the session information and information indicating an abort request, and outputs abort request information containing the session information, the information indicating the abort request, and the electronic signature, whereby transmission/reception can be performed without unnecessary information. Similarly, it may be configured to use only the second session information to generate an electronic signature for information containing the session information and information indicating a commitment request, and to output commitment request information containing the electronic signature. Since a third-party device defines a third session state as abort in correspondence to the second session information, it is able to manage states while appropriately discriminating a plurality of concurrent electronic value exchanges.