There are proposed: a network system capable of realizing packet forwarding higher in packet forwarding efficiency than in conventional Intermittent Periodic Transmit (IPT) using omni-directional antennas; and the like. Directional antennas are applied to the IPT, and each of slave nodes waits for reception of downlink packets by a directional antenna for receiving the downlink packets in a reception waiting state therefor. Moreover, the downlink packets are treated like polling control signals, and uplink packets are transmitted at a reception time of the downlink packets, whereby a hidden node problem and a carrier sensing problem can be avoided. Furthermore, in accordance with routing protocol in which each of nodes changes directivity randomly by a route formation process, it becomes possible to form a more suitable route.