An on-board device comprising an on-board communication device for communicating with a ground communication device; and a speed detection device arranged to detect a vehicle speed; wherein when the vehicle speed detected by the speed detection device is equal to or lower than a predetermined value, the on-board communication device is configured to determine that the on-board communication device is present within a communication range of the ground communication device when a signal magnetic field intensity of a signal from the ground communication device received by the on-board communication device is higher than a first threshold, and to determine that the on-board communication device is present outside the communication range of the ground communication device when the signal magnetic field intensity of the signal from the ground communication device received by the on-board communication device is lower than a second threshold smaller than the first threshold, wherein when the vehicle speed detected by the speed detection device is higher than the predetermined value, the on-board communication device is configured to determine that the on-board communication device is present within the communication range of the ground communication device when the signal magnetic field intensity of the signal from the ground communication device received by the on-board communication device is higher than a third threshold, where the third threshold is smaller than the first threshold and greater than the second threshold, and to determine that the on-board communication device is present outside the communication range of the ground communication device when the signal magnetic field intensity of the signal from the ground communication device received by the on-board communication device is lower than the third threshold. to determine that the on-board communication device is present within a communication range of the ground communication device when a signal magnetic field intensity of a signal from the ground communication device received by the on-board communication device is higher than a first threshold, and to determine that the on-board communication device is present outside the communication range of the ground communication device when the signal magnetic field intensity of the signal from the ground communication device received by the on-board communication device is lower than a second threshold smaller than the first threshold, wherein when the vehicle speed detected by the speed detection device is higher than the predetermined value, the on-board communication device is configured to determine that the on-board communication device is present within the communication range of the ground communication device when the signal magnetic field intensity of the signal from the ground communication device received by the on-board communication device is higher than a third threshold, where the third threshold is smaller than the first threshold and greater than the second threshold, and to determine that the on-board communication device is present outside the communication range of the ground communication device when the signal magnetic field intensity of the signal from the ground communication device received by the on-board communication device is lower than the third threshold.