Detecting a fraudulent mobile station in a mobile communication system using location information of mobile station

(57) Summary book invention relates to the mobile communication system equipped with the move station (MS, MS'), the move exchange center (MSC1), and the member register (VLR1) containing subscriber data including the position information which directs the position of a move station. In order to detect existence of an unjust move station, this system, The surveillance means (1) for supervising the process of causing change of the position information in the above-mentioned member register (VLR1), When change of position information is caused by the process which should cause change of the position information in the above-mentioned member register (VLR1) and which does not come out, it has the detection means (2) for detecting and directing existence of an unjust move station (MS').