A location register 13 stores as location information of a relay device 21 to area identification information of a location registration area where relay device 21 is currently located and stores as location information of one or a plurality of mobile communication terminals 7 transported in a moving object 2, relay device identification information of relay device 21 to thereby subordinate one or more of a plurality of mobile communication terminals 7 to relay device 21. In the case that a master/slave relationship should be discontinued with some of a plurality of mobile communication terminals 7, relay device 21 transmits, to location register 13, a dependency registration removal request specifying the part of a plurality of mobile communication terminals 7. Location register 13 updates location information of the mobile communication terminals 7 specified in the dependency registration removal request to area identification information of a location registration area in which relay device 21 is currently located.