PURPOSE: To always recognize a receiving port without any error.

CONSTITUTION: A regenerative repeating part 1 regeneratively repeats a frame to twisted pair wire interfaces 8a-8d, a communication control part 2, a repeating frame detecting part 3, and a transmission origin address storage part 4. The repeating frame detecting part 3 transmits a detection signal 12 to a transmission origin address storage part 4 and a receiving port storage part 5. The transmission origin address detecting part 4 stores the transmission origin address of the repeating frame synchronously with the detection signal 12. Similarly, the receiving port storage part 5 stores receiving port information from the regenerative repeating part 1 synchronously with the detection signal 12. A microcomputer 7 can find the address of a terminal connected with the stranded wire interfaces by obtaining those synchronously stored transmission origin address and receiving port information. Thus, the information of the transmission origin address and the receiving port can be obtained synchronously with the same signal.