An apparatus corrects a position coordinate measured by a GPS receiver. Road data representing a position coordinate of a constructed road is included. Locus data representing a plurality of position coordinates of the GPS receiver during a past specified period is generated based on a position coordinate acquired. A road section traveled by the GPS receiver during the past specified period is estimated based on road data stored and a position coordinate acquired. A bias error of a position coordinate measured by the GPS receiver is estimated based on position coordinates at a plurality of points in a road section estimated and position coordinates at a plurality of points represented by the locus data. A position coordinate measured by the GPS receiver is corrected based on a bias error estimated and outputted.