A mobile communication system comprises base stations, a mobile terminal and a control device. The mobile terminal comprises a report unit reports a reception power of a radio wave from a current station and a next station to the control device for each base station switch processing. The control device comprises a calculation unit calculates a first distance and a second distance. The first distance is the distance between the current station and the mobile terminal. The second distance is the distance between the next station and the mobile terminal. The control device comprises a database stores distance data between the base stations. The control device comprises an update unit updates the distance data by a minimum value of a sum of the first and the second distances.