A network system, radio communication device, radio communication method, and computer program for same are provided. The present invention enables formation of a network topology with sensor nodes each having a traveling function and operating in the self-directive and dispersive state without using positional information. Each sensor nodes periodically transmits a HELLO message to neighboring nodes to exchange information therewith. In an area where the node density is high, the nodes are set in the Expand state and in the Bridge state. A node in the Expand state shifts to the Stay state when the node can be connected to only one neighboring node to becomes a component of the topology. A node in the Bridge state shifts to the Stay state together with neighboring nodes each having hidden terminals not less than a prespecified number to become a component of the topology.