When a CPU core 53 of a node detects change of data which comes into the node from a load 60 connected thereto on the input side, and thereby the CPU core 53 and a transmission control circuit 52 wake up, the node transmits a frame for waking-up to a transmission line 4. However, when the node receives a frame for waking-up from another node via the transmission line 4 and thereby wakes up, the node does not transmit a frame for waking-up. Thus, an increase in traffic at the time of waking up is reduced and data transmission in a normal operation mode is started soon, so that the speed of data transmission is increased.