To obtain a device that enables fault detection and automatic switching of line even in a duplex line communication device which has nodes connected in many stages.

The duplex line communication device which has a plurality of nodes 1 mutually connected by duplex lines is provide with a means which transmits a health check packet to each object node 1 with a prescribed period, a means which receives the health check packet transmitted from each object node to discriminate whether each system of duplex lines is normal or not with respect to each object node, a system selection memory 4 in which normality/abnormally discrimination result of each system of each object node is preserved, and a means which selects a system for data reception in each object node in accordance with contents of the system selection memory.