An on-board device is mounted on a train having a battery capable of supplying power when a vehicle power supply is off, a parking brake to fix a wheel when the train is stopped, and a parking-brake controlling electromagnetic valve to be energized by power supplied from the battery when the parking brake is released, and even when the vehicle power supply is off, retains position information of the train stored when the vehicle power supply is on. The on-board device includes a parking-brake release detecting circuit that has a parking-brake-controlling-electromagnetic-valve energization detecting unit to detect energization to the parking-brake controlling electromagnetic valve when the vehicle power supply is off, and a parking-brake-controlling-electromagnetic-valve energization detection storage unit to store therein a result of detection until stored contents are reset.