PURPOSE: To correctly recognize connection relation even when the line concentration device is hierarchically connected by recording the transmission destination address of a frame for constitution recognition and erasing the frame from a transmission line when the frame is received.

CONSTITUTION: A frame transmission part 20 of the line concentration device 10 has a constitution recognition frame transmission part 30 which sets its address as a transmission source address in the frame for constitution confirmation distinctive from other general frames and sends them. Further, a frame reception part 40 has a constitution confirmation frame reception part 50 which records transmission source address of the frame and erases the frame from the transmission line when the frame for constitution recognition is received. This constitution recognition frame transmission part 30 sends the frame for constitution recognition where its address is set to all ports P1-P3. Therefore, remote constitution management of the line concentrating device can be performed without requiring any operator and a management device which is flexibly applied to a network having many changes can be designed.