The present invention proposes a network system, etc., that are suitable for improving the communication efficiency of an entire network even when a CSMA, etc., are adopted. A network system for transmitting uplink/downlink traffics using a route having a tree structure with a root node, a plurality of inner nodes, and a plurality of leaf nodes, wherein the root node transmits a downlink frame to the inner nodes and leaf nodes at intervals equal to or greater than an additional wait time differing for each destination node. The root node transmits a downlink frame at, for example, an interval consisting of the additional wait time plus a quality assurance time for assuring communication quality. An interval which is a varying time interval but equal to the additional wait time at the least is assured, whereby the communication efficiency of an entire network is improved.