In a communication system formed of two or more networks in which a part or all of nodes belonging to each said network form a plurality of combinations of nodes so as not to overlap with other node on the network to which each node belongs, the nodes belonging to the same combination are connected with each other and terminals are connected under the control of a part or all of the nodes belonging to the same combination, a node belonging to the combination transmits a frame received from a terminal under the control of the node itself to any of adjacent nodes on the network to which the node itself belongs and a node belonging to the same combination to which the node itself belongs and connected to the node itself. This obtains a highly reliable communication system whose desired transmission capacity can be realized at low costs and which can be restored from an abnormal state in a short time period.