Estimation calculations for calculating an estimated present position are performed twice corresponding to each satellite set. The estimated present position calculated by the second estimation calculations is determined to be a present position candidate corresponding to the target satellite set. In the first estimation calculations corresponding to the first satellite set, the calculated satellite position and estimated pseudo-range of each GPS satellite are stored in caches. In the second estimation calculations, the satellite position of each GPS satellite is read from the cache. In the first estimation calculations corresponding to the second or subsequent satellite set, the satellite position and the estimated pseudo-range of each GPS satellite are read from the caches, and the satellite position and the estimated pseudo-range of the GPS satellite of which the satellite position and the estimated pseudo-range have not been stored in the caches are calculated and stored in the caches. In the second estimation calculations, the satellite position of each GPS satellite is read from the cache.