To provide a mobile station positioning system uninfluenced by fluctuation of transmission power of a radio wave by a mobile station, and utilizing reception power of the radio wave.

A difference of reception power between pairing base stations is calculated by a distance ratio calculation part 54, based on the reception power measured respectively by a reception power measuring part 38 in a base station, when a radio wave transmitted from the mobile station is received by each base station, and a distance ratio between a distance from one base station to the mobile station and a distance from the other base station to the mobile station is calculated based on the difference of the reception power. A locus which is a series of points showing each position realizing the calculated distance ratio is generated by a locus generation part 56, and intersection points of each locus relative to a plurality of base station pairs are calculated by a position calculation part 58, to thereby calculate candidates of the existence position of the mobile station.