A train detector for detecting presence of a first train and a second train on a track respectively, by transmitting a train detection signal to a dual gauge track circuit having a standard track rail, a narrow track rail and a common rail, the first train traveling on the standard track rail and the common rail, and the second train traveling on the narrow track rail and the common rail, wherein the train detector comprises: a common transmitter for transmitting a first train detection signal having a predetermined frequency to the standard track rail and a second train detection signal having a frequency different from the first train detection signal to the narrow track rail; a common receiver for receiving the first train detection signal from the standard track rail and the second train detection signal from the narrow track rail; a first filter connected between the standard track rail and the common receiver and designed to pass a frequency band of the first train detection signal and to increase an impedance at a frequency band of the second train detection signal so as to suppress a current of the second train detection signal; a second filter connected between the narrow track rail and the common receiver and designed to pass a frequency band of the second train detection signal and to increase an impedance at a frequency band of the first train detection signal so as to suppress a current of the first train detection signal; a third filter connected between the common transmitter and the standard track rail and designed to pass a frequency band of the first train detection signal and to increase an impedance at a frequency band of the second train detection signal so as to suppress the current of the second train detection signal in the standard track rail; and a fourth filter connected between the common transmitter and the narrow track rail and designed to pass a frequency band of the second train detection signal and to increase an impedance at a frequency band of the first train detection signal so as to suppress the current of the first train detection signal in the narrow track rail, characterised in that the train detector has both of a train detection function and a train control function: by setting the frequency of a train control signal in a band range in the middle of the frequencies of the first train detection signal and the second train detection signal, and in the band range that passes the first, second, third, and fourth filters, and by transmitting the train control signal from the common transmitter to the standard track rail and the narrow track rail. a common transmitter for transmitting a first train detection signal having a predetermined frequency to the standard track rail and a second train detection signal having a frequency different from the first train detection signal to the narrow track rail; a common receiver for receiving the first train detection signal from the standard track rail and the second train detection signal from the narrow track rail; a first filter connected between the standard track rail and the common receiver and designed to pass a frequency band of the first train detection signal and to increase an impedance at a frequency band of the second train detection signal so as to suppress a current of the second train detection signal; a second filter connected between the narrow track rail and the common receiver and designed to pass a frequency band of the second train detection signal and to increase an impedance at a frequency band of the first train detection signal so as to suppress a current of the first train detection signal; a third filter connected between the common transmitter and the standard track rail and designed to pass a frequency band of the first train detection signal and to increase an impedance at a frequency band of the second train detection signal so as to suppress the current of the second train detection signal in the standard track rail; and a fourth filter connected between the common transmitter and the narrow track rail and designed to pass a frequency band of the second train detection signal and to increase an impedance at a frequency band of the first train detection signal so as to suppress the current of the first train detection signal in the narrow track rail, characterised in that the train detector has both of a train detection function and a train control function: by setting the frequency of a train control signal in a band range in the middle of the frequencies of the first train detection signal and the second train detection signal, and in the band range that passes the first, second, third, and fourth filters, and by transmitting the train control signal from the common transmitter to the standard track rail and the narrow track rail. by setting the frequency of a train control signal in a band range in the middle of the frequencies of the first train detection signal and the second train detection signal, and in the band range that passes the first, second, third, and fourth filters, and by transmitting the train control signal from the common transmitter to the standard track rail and the narrow track rail.