Monitoring device for multiplex data communication equipment

A monitoring device for multiplex transmitters preferably used for composed vehicles accurately monitors abnormal condition of slave devices regardless of erroneous multiplex data communication between a master device (101) and the slave devices (102,103). The monitoring device according to the present invention comprising: a master device; a plurality of slave devices multiply communicated with the master device; control means (8,9) connected to the plurality of slave devices each, the controlled means (7) controlled by command signals from the master device; master memory (4) provided to the master device for sequentially storing the command signals transmitted to the plurality of slave devices and state signals indicating condition of the controlled means of the slave device each; slave memories (11a) each provided to the plurality of slave devices each for sequentially storing command signals received by the slave devices and the state signals indicating condition of the slave device, timing signals generated in the master device, the timing signals transmitted to the slave memories each, the timing signals stored in the master memory and the slave memories each according to stored content of the master memory and the slave memories each; and a memory output means (12) for reading out and displaying the command signals and timing signals stored in the master device and the received command signals, the state signals, and timing signals stored in the slave memories.