A communication network system including a plurality of nodes disposed on a communication bus, and where each of the nodes is capable of transitioning between a normal operation mode and a low electricity consumption mode. The communication network system controls only a required node, in order to communicate with such required node, by transitioning the required node from the low power mode to the normal operation mode. To control the mode of the required nodes, a controlling node keeps a signal change state of the communication bus for a period that is longer than a normal communication frame length. The required node determines whether the period of the signal change state is longer than a threshold of the required node itself, to output a wakeup signal to a control circuit.