PURPOSE: To attain a high density operation and to shorten the time interval between trains by providing a returning path for a signal current along rails, providing a transmitter-receiver between the rail and the return so as to use it for data transmission/reception with trains.

CONSTITUTION: A transmitter 1 has a function of generating a serial data for train control and of modulating the data into an FSK signal and is provided between one rail r2 and one end of a return (a). Moreover, a receiver 2 has a function of democulating a signal sent from a train to ground and is provided between the rail r2 and the other end of the return (a). A signal sent from trains T1, T2 on the rails to the receiver 2 flows through the rail r2 and the return (a) and is inputted to the receiver 2. Since a train position data is sent to the rail r2 through a transmission/reception antenna 3 based on the signal of a tachometer generator G from a preceding train T1, the position data of the preceding train T1 is fetched directly by the succeeding train T2 and the operation of plural trains is attained between a couple of transmitters-receivers.