An onboard system measures the train position by measuring the rotational speed of a tacho-generator, determines an estimated train occupancy range (in which the train may be present) using the train position, and transmits the estimated train occupancy range to a ground system. The onboard system corrects the train position based on the results of communication with a correction coil when the train has passed through the installation point of a correction coil. When the train position has been shifted backward as a result of correction that utilizes the correction coil, the onboard system determines and transmits the estimated train occupancy range based on the train position immediately before correction until the latest train position reaches the train position immediately before correction, and determines and transmits the estimated train occupancy range based on the latest train position after the latest train position has reached the train position immediately before correction.
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