Intrusion detecting system, intrusion detecting method and defectiveness detecting method

The present invention provides a method of judging a trouble and deducing the location where a trouble exists in the case that the received signal at receiver fluctuates because of the defects occurred in a leakage cable and the related machine(s) thereof, but without misdetecting as an intrusion. The method judges whether wave launching means 201 or wave receiving means has a defect when the decreased breadth of amplitude of the received signal in comparison with the transmitted signal exceeds a specified ratio, with regard to a range bin corresponding to the remote end, in the range bins wherein the received signals are correspondent to the distances from the electrically feeding ends of wave launching means 201 and wave receiving means 301, by means of the correspondence between the delay time from the sending time of transmitted signal to the receiving time of received signal and the distance of propagation path depending on the passing location of propagation of the received signals in the wave launching