A road information generating apparatus, comprising: a host vehicle position information acquiring unit adapted to acquire host vehicle position information that indicates a position of a host vehicle (c); an image information acquiring unit adapted to acquire image information that includes a road along which the host vehicle (c) is traveling, the image information acquiring unit comprising a camera mounted on the host vehicle (c); and a host vehicle travel lane detecting unit adapted to detect a host vehicle travel lane along which the host vehicle (c) is traveling and other vehicle travel lanes by extracting an image of a boundary of the lanes from the image information, characterized in that detecting the host travel lane comprises determining a position of the host travel lane relative to the other vehicle travel lanes in terms of a number of the host vehicle travel lane, and determining whether or not the host vehicle lane and the other lanes can be specified; the road information generating apparatus further comprising a lane information registering unit adapted to determine, responsive to a determination that the host vehicle travel lane and the other lanes can be specified, whether or not the host vehicle is travelling along substantially the transverse center of the host vehicle travel lane, and, when it has been determined that the host vehicle is travelling along the transverse center of the host vehicle travel lane to acquire the host vehicle position information, to generate lane information by setting the position of the host vehicle to a node or a contour interpolation point, and to register the generated lane information on a storage medium, and, when it has been determined that the host vehicle is not travelling along the transverse center of the host vehicle travel lane to acquire the host vehicle position information, to specify the transverse center position of the lane by compensating for that position that is given by the host vehicle position information, to generate lane information by setting the center position to the position of a node or a contour interpolation point, and to register the generated lane information on the storage medium, wherein the lane information indicates the position of the host vehicle travel lane relative to the other vehicle travel lanes in terms of a number of the host vehicle lane. a host vehicle position information acquiring unit adapted to acquire host vehicle position information that indicates a position of a host vehicle (c); an image information acquiring unit adapted to acquire image information that includes a road along which the host vehicle (c) is traveling, the image information acquiring unit comprising a camera mounted on the host vehicle (c); and a host vehicle travel lane detecting unit adapted to detect a host vehicle travel lane along which the host vehicle (c) is traveling and other vehicle travel lanes by extracting an image of a boundary of the lanes from the image information, characterized in that detecting the host travel lane comprises determining a position of the host travel lane relative to the other vehicle travel lanes in terms of a number of the host vehicle travel lane, and determining whether or not the host vehicle lane and the other lanes can be specified; the road information generating apparatus further comprising a lane information registering unit adapted to determine, responsive to a determination that the host vehicle travel lane and the other lanes can be specified, whether or not the host vehicle is travelling along substantially the transverse center of the host vehicle travel lane, and, when it has been determined that the host vehicle is travelling along the transverse center of the host vehicle travel lane to acquire the host vehicle position information, to generate lane information by setting the position of the host vehicle to a node or a contour interpolation point, and to register the generated lane information on a storage medium, and, when it has been determined that the host vehicle is not travelling along the transverse center of the host vehicle travel lane to acquire the host vehicle position information, to specify the transverse center position of the lane by compensating for that position that is given by the host vehicle position information, to generate lane information by setting the center position to the position of a node or a contour interpolation point, and to register the generated lane information on the storage medium, wherein the lane information indicates the position of the host vehicle travel lane relative to the other vehicle travel lanes in terms of a number of the host vehicle lane.