Set of Gateway devices (2, 3) for relaying data communication between a host connected thereto via a wired network, which he monitors and controls, and a plurality of wireless nodes (41 to 48) connected thereto via a wireless circuit and constituting a wireless network, each one of said gateway devices (2; 3) comprising: wireless communication means for sending data from the host to at least any one of the wireless nodes (41 to 48); redirect means for causing the wireless communication means to send the data to one of the wireless nodes (41 to 48) and to transfer the data to the other of the set of gateway devices (3; 2) connected to the wired network; wired communication means for implementing data send/receive between the host and. the other gateway device (3 or 2) via the wired network, storage means for storing therein the wireless node list and routing information; and routing means, characterized in that communication protocol conversion means are provided mutually converting between communication data based on a communication protocol employed by the wired network and communication data based on a communication protocol employed by the wireless network; the wireless communication means sends data from the host, that is converted into communication data based on the communication protocol employed by the wireless network, by the communication protocol conversion means, to the wireless node selected by the routing means; and the routing means for selecting a wireless node constituting a communication route in desired excellent communication quality and extend from a first corresponding gateway device (2; 3) to the wireless node serving as the final destination as a wireless node of the next hop to which data is sent based on the data from the host and the wireless node list, extracts the final destination node from data received from the host and selects the wireless node constituting an optimum mesh network route. wireless communication means for sending data from the host to at least any one of the wireless nodes (41 to 48); redirect means for causing the wireless communication means to send the data to one of the wireless nodes (41 to 48) and to transfer the data to the other of the set of gateway devices (3; 2) connected to the wired network; wired communication means for implementing data send/receive between the host and. the other gateway device (3 or 2) via the wired network, storage means for storing therein the wireless node list and routing information; and routing means, characterized in that communication protocol conversion means are provided mutually converting between communication data based on a communication protocol employed by the wired network and communication data based on a communication protocol employed by the wireless network; the wireless communication means sends data from the host, that is converted into communication data based on the communication protocol employed by the wireless network, by the communication protocol conversion means, to the wireless node selected by the routing means; and the routing means for selecting a wireless node constituting a communication route in desired excellent communication quality and extend from a first corresponding gateway device (2; 3) to the wireless node serving as the final destination as a wireless node of the next hop to which data is sent based on the data from the host and the wireless node list, extracts the final destination node from data received from the host and selects the wireless node constituting an optimum mesh network route.