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1. A mobile communication system that includes a first base station transmitting adjacent base station information and a mobile station communicating with the first base station, the mobile communication system comprising:
a transmitting unit that repeatedly transmits, from the first base station to the mobile station, at least three pieces of area information set for a plurality of areas including a first area, a second area and a third area obtained by dividing a radio wave transmission range of the first base station, a first piece of the area information including an identifier of a base station installed in the first area and range information of other areas including the second and third areas, a second piece of the area information including an identifier of a base station installed in the second area and range information of other areas including the first and third areas, a third piece of the area information including an identifier of a base station installed in the third area and range information of other areas including the first and second areas; a rough position acquiring unit that acquires a rough position of the mobile station, the rough position being obtained by communication between the mobile station and the first base station; a selecting unit that selects, based on the at least three pieces of the area information repeatedly transmitted by the transmitting unit, one or more base stations whose information is not included in the adjacent-base-station information but included in a piece of the area information set for one of the areas to which the rough position obtained by the rough position acquiring unit belongs, when the rough position does not belong to ranges of the other areas indicated by the range information included in the piece of the area information; and a position detecting unit that, by using the one or more base stations selected by the selecting unit, detects a position of the mobile station.
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