1. A gateway device connecting a plurality of networks utilizing different protocols, the protocols including at least a first protocol and a second protocol, said gateway device comprising: a template holding unit holding a template (i) described based on a standard used by the second protocol, and (ii) for having information regarding a terminal appliance written therein, the terminal appliance being connected to a network, of the plurality of networks, that utilizes the first protocol; an obtainment unit obtaining, from the terminal appliance connected to the network utilizing the first protocol, the information regarding the terminal appliance, the information regarding the terminal appliance being based on a standard used by the first protocol; a template description creation processing unit creating a terminal appliance information description by (i) obtaining the template held in said template holding unit, and (ii) writing the information regarding the terminal appliance in the template; a protocol conversion table holding unit holding a protocol conversion table, the protocol conversion table storing (i) a representative format of the information regarding the terminal appliance in the first protocol, and (ii) a representative format of the information regarding the terminal appliance in the second protocol, such that the representative format of the information regarding the terminal appliance in the first protocol and the representative format of the information regarding the terminal appliance in the second protocol are associated with a name of the terminal appliance; a protocol conversion unit performing a protocol conversion when a control device connected to a network, of the plurality of networks, that utilizes the second protocol performs communications with the terminal appliance connected to the network utilizing the first protocol, the protocol conversion being performed by referring to the protocol conversion table; and a communication unit transmitting the terminal appliance information description to the control device connected to the network utilizing the second protocol, the terminal appliance information description being updated by said template description creation processing unit.