PROBLEM TO BE SOLVED: To provide a technique allowing a plurality of communication relay devices to efficiently manage a plurality of devices.SOLUTION: A communication system 1 comprises, on a LAN 107, a plurality of devices 10 and a plurality of gateways 30 (30a and 30b). The gateway 30a performs a device search process of searching for devices on the LAN 107 and obtains information (management device information) on a second management object device (a device whose communication relay process with a server 70 (not on the LAN 107) is managed by the different gateway 30b). After excluding at least a part of an overlap of a first management object device (a device whose communication relay process with the server 70 is managed by the gateway 30a) and the second management object device on the basis of the management device information and two or more devices found by the device search process, the gateway 30a determines a first management object device.SELECTED DRAWING: Figure 6