Disclosed is a system including a plurality of node devices connected to a network, in which in the node device, each transmit a packet for transferring noise information so that any of the node devices on the network is able to grasp the noise information. The signal level of a received signal from a transmission line is monitored by a monitor circuit and analyzed by a sampling analysis unit. Based on the result of analysis, a packet for transferring noise information is generated by a noise information transfer packet generator and controlling unit and the generated packet is sent out from an output circuit to a transmission line. On receipt of the packet for transferring noise information, sent over the transmission line, the controlling unit extracts the noise information from the packet to supply the extracted noise information to a correction command circuit.