PROBLEM TO BE SOLVED: To provide a fail-safe property for a GPS electric wave shutting-off object detection system utilizing GPS electric wave in order to enable application to a railway signal field or the like. SOLUTION: GPS antenna 11 and GPS receiver 12 are made to general purpose articles, a determination device 13 in which success or failure of receiving of the electric wave is determined based on the output, it is determined at success of receiving that GPS electric wave shutting-off object does not exist and it is determined at failure of receiving that the GPS electric wave shutting-off object exists is constituted by a fail-safe device. The whole of the system is made to a fail-safe system by monitoring soundness of the GPS ground devices 11, 12 and its transmission system by the determination device. Further, in addition to existence of receiving of such an electric wave, comparison of a position measurement result with a memory position and property distinction of renewal of the time are also performed to produce determination at the safety side. COPYRIGHT: (C)2009,JPO&INPIT
