A low cost communication apparatus enables detection of an apparatus present on a different network in a router multistage network having a plurality of routers. When a communication apparatus cannot detect, on a network thereof, a desired apparatus, the communication apparatus requests a connection support server securing communication paths with all the apparatuses on a home network, to relay an apparatus detection request. The connection support server transfers the request to relay the apparatus detection request, to an arbitrary apparatus belonging to a different network from the network to which the communication apparatus belongs, and the arbitrary apparatus, by proxy, performs an apparatus detection, and transfers information about a detected apparatus to the connection support server. By obtaining the information from the connection support server, the communication apparatus detects the apparatus on the different network.