PURPOSE: To provide a vehicle detecting device of an on-vehicle signal receiving system capable of detecting failure of ground devices with a simplified composition.

CONSTITUTION: A transmitter 11 generates an on-vehicle signal F1 and an on- vehicle piece 12 transmits the on-vehicle signal F1. Ground antennas 211 to 213 are successively provided in the proceeding direction X of a vehicle 4. When the on-vehicle piece 12 passes the closed boundary part of the adjacent two blocked sections 1T, 2T, adjacent ground antennas 211, 212 simultaneously receives the on-vehicle signal F1 and output received signals 1F1, 2F1 which mutually overlap with time lag. A signal processing circuit 22 forms signals 1TF1, 2TF1 of two values, which mutually overlap with time lag, based on received signals 1F1, 2F1 and outputs vehicle detecting signals 1TR, 2TR in accordance with the logical judgment of such signals. The same applies to the case when the on-vehicle piece 12 passes the blocked boundary part of the blocked section 2T, 3T.