To enhance the noise resistance of a train detecting device by extracting a PN code by demodulating a received diffusion signal by using a transmission signal, and detecting the presence of a train on rails from a coincident state of an extracted extraction signal and the PN code.

First of all, when a train does not exist in a stoppage section T5, a carrier wave sent out of a signal generator 1 becomes a diffusion signal by performing diffusion processing by using a PN code by a diffusion circuit 2 to be supplied to the starting end side A of rails via a transmitter 3. After being amplified by a receiver 5, this diffusion signal is demodulated by using the carrier wave by a demodulating circuit 6, the diffusion signal is taken out, and the former PN code is extracted. Afterwards, a detector 8 turns on a track relay TR when the PN code exists in output of a filter circuit 7. While, when the train exists in the stoppage section T1, the detector 8 cannot maintain ON of the track relay TR, so that the track relay TR is turned off. The presence of the train can be known by OFF of the track relay TR.