A line status monitoring circuit receives a frame through one of a number of lines from another node connected through a redundant transmission channel which is made redundant by the lines. The line status monitoring circuit includes a line-specific check frame monitoring unit. If a line-specific check frame having an added dedicated header corresponding to each of the plurality of lines is received through one of the lines from another node, the line-specific check frame monitoring unit determines whether or not a further line-specific check frame corresponding to a frame for checking which is identical to a frame for checking to which the line-specific check frame corresponds is received through at least a predetermined number of lines within a predetermined time. If the further line-specific check frame is not received in this manner, the line-specific check frame monitoring unit discards the frame.