1. A navigation apparatus comprising: a current position detector for producing data of a current location of a mobile body on the basis of at least one of navigation parameters of the mobile body and measurement data supplied from a plurality of artificial satellites; a storage device for storing map data which includes road data representing one route on a road, the map data also including additional road data for a predetermined region on the road, the additional road data representing another route on the road other than the one route; and a map matching device for applying a map matching process to the data produced by the current position detector, using the road data, to determine the current location of the mobile body when the mobile body is not adjacent to the predetermined region, and for applying the map matching process to the data produced by the current position detector, using one of the additional road data and the road data depending upon a moving condition of the mobile body, to determine the current location of the mobile body when the mobile body is adjacent to or in the predetermined region.