PURPOSE: To operate a vehicle in a failsafe manner by transmitting a parallel signal of security and safety information converted to excitation signals and general information of DC level and deciding as a normal significant signal the fact that there is excitation signal at a receiver side.

CONSTITUTION: A converter 3 converts an input signal S1a into an excitation signal S3. A transmission controller 5 converts the excitation signal S3 and DC level signals S1b, S1c into serial data signal S4, and transmits it. A receiver station 2 converts the serial data signal S4 into parallel signals S6aWS6c. An AC amplifier 10 drives a relay 12a when the signal S6a is an excitation signal to close an output instruction contact 13a and outputs an excitation signal S7a. When this signal S7a is not outputted, it is judged as a malfunction, thereby operating an emergency brake to prevent a train for rolling or run away.