1. A gateway device that connects two or more networks having different protocols, the protocols including at least a first protocol and a second protocol, said gateway device comprising: a template holding unit which holds a template which is described based on a standard used for the second protocol and in which information regarding a terminal appliance connected to a network having the first protocol is to be written; an obtainment unit operable to obtain, from the terminal appliance connected to the network having the first protocol, the information regarding the terminal appliance which is based on a standard used for the first protocol; a template description creation processing unit operable to create a terminal appliance information description by obtaining the template held in said template holding unit and writing the information regarding the terminal appliance in the template, the information being obtained by said obtainment unit; a protocol conversion table holding unit which holds a protocol conversion table in which representation formats of the information corresponding to the terminal appliances in the first protocol and the second protocol respectively are associated with names of the terminal appliances; a protocol conversion unit operable to convert a protocol in the case where a control device connected to the network having the second protocol performs communications with the terminal appliance connected to the network having the first protocol by referring to the protocol conversion table; and a communication unit operable to transmit the terminal appliance information description to the control device connected to the network having the second protocol, the description being updated by said template description creation processing unit.