A train protection device, which decides a position of an own train on track by using GPS satellites, includes: a GPS reception unit; a tachogenerator unit; a track-information storage unit; and a position decision unit. The position decision unit decides the position of the own train based on the GPS signal, the reception state value, the running distance from the reference position, the current speed, and the information of a track on which the own train runs. When the reception state value is equal to or larger than a threshold, the position decision unit decides a position as a current train position by adding, with respect to a forward direction of the track on which the own train runs, a correction value.