An automatic train protection system for detecting a position of a train at a trackside system on the basis of train control information including train position information, the automatic train protection system comprising: an onboard system configured to control the whole train and to communicate with the trackside system; an onboard power supply device configured to supply power to the whole train and to generate a previous power shutdown signal providing an advance notice of shut-off of power supply to the onboard system; an onboard storage device configured to store position information of the train; an onboard speed measuring device configured to measure the speed of the train; and the trackside system; wherein the automatic train protection system is configured such that: the train control information is stored on the storage device in response to occurrence of the previous power shutdown signal; the train position information recorded on the storage device is transmitted to the trackside system when power supply to the onboard system is started; and the train control information stored on the storage device is deleted when a predetermined condition is satisfied; and wherein the predetermined condition is one of: while the train control information is stored on the storage device, the speed measuring device detects running of the train before the power supply is shut off; while the train control information is stored on the storage device, power supply to the train is resumed and the train control information is read from the storage device; and while the train control information is stored on the storage device, power supply to the train is resumed and the stored train control information is read from the storage device and transmitted to the trackside system. an onboard system configured to control the whole train and to communicate with the trackside system; an onboard power supply device configured to supply power to the whole train and to generate a previous power shutdown signal providing an advance notice of shut-off of power supply to the onboard system; an onboard storage device configured to store position information of the train; an onboard speed measuring device configured to measure the speed of the train; and the trackside system; wherein the automatic train protection system is configured such that: the train control information is stored on the storage device in response to occurrence of the previous power shutdown signal; the train position information recorded on the storage device is transmitted to the trackside system when power supply to the onboard system is started; and the train control information stored on the storage device is deleted when a predetermined condition is satisfied; and wherein the predetermined condition is one of: while the train control information is stored on the storage device, the speed measuring device detects running of the train before the power supply is shut off; while the train control information is stored on the storage device, power supply to the train is resumed and the train control information is read from the storage device; and while the train control information is stored on the storage device, power supply to the train is resumed and the stored train control information is read from the storage device and transmitted to the trackside system. while the train control information is stored on the storage device, the speed measuring device detects running of the train before the power supply is shut off; while the train control information is stored on the storage device, power supply to the train is resumed and the train control information is read from the storage device; and while the train control information is stored on the storage device, power supply to the train is resumed and the stored train control information is read from the storage device and transmitted to the trackside system.