A mobile communication system includes a first base station and one or more base stations whose information is included in adjacent-base-station information notified by the first base station. The mobile communication system includes a transmitting unit that transmits information on one or more base stations whose information is not included in the adjacent-base-station information to a mobile station, and a position detecting unit that, by using the one or more base stations whose information is not included in the adjacent-base-station information, detects a position of the mobile station.