A gateway apparatus relays a data packet only when a network that is connected to the gateway apparatus itself is identical to a network that is connected to a node associated with a sender's address. The sender's address is carried in the data packet received. Even if there are accesses from a plurality of nodes to a certain node (e.g., sensor node), the gateway apparatus can relay the data packet such that data retrieval takes place appropriately and/or such that node control takes place appropriately.