PURPOSE: To send simple management information between hubs even when at least one of the hubs has no management function by sending/receiving simple management information as voltage information and detecting the information.

CONSTITUTION: Simple management information generated by a management information transmission means 15 of a management information sender side board 1 is applied to a management information reception port 2 as a voltage between a common mode voltage of a sender side twisted pair wires 3a and a common mode voltage of a receiver side twisted pair wires 3b. The management information reception port 2 detects the voltage between the common mode voltage of the sender side twisted pair wires 3a and the common mode voltage of the receiver side twisted pair wires 3b. The detected voltage is converted into simple management information data by a management information reception means 25. Thus, the simple management information is sent between hubs being components of the network even when either of them has no management capability.