The mobile communication network system having a plurality of mobile communication systems each including a base station performing wireless communications with a mobile station, comprises a storage unit storing location information of the mobile station, an acquisition unit acquiring, when receiving a location registering request from the mobile station, a communication-enabled mobile communication system in the mobile station as a sender of the location registering request, a specifying unit specifying a base station existing within the acquired communication-enabled mobile communication system and existing in the periphery of the base station receiving-the location registering request, and a control unit storing the storage unit with information of the base station receiving the location registering request and information of the specified base station as location information about the sender mobile station of the location registering request.