1. A navigation apparatus comprising: a sensor for detecting a behavior of a vehicle; a positioning means for estimating the behavior of the vehicle on a basis of a signal from said sensor; a road-map-data storage means for storing road data; a road matching means for comparing positioning data sent thereto, as an estimation result, from said positioning means with the road data read from said road-map-data storage means so as to identify a current position of the vehicle, and for judging whether the identification is placed in a matching state in which the current position is finally identified as being on a road defined by the road data (referred to as a “registered road” from here on), in a pending state in which whether or not the current position is on a registered road is being judged, or in a free state in which the current position is finally identified as being out of any registered road, and then outputting matching result data indicating the state of the identification; an unregistered road detecting means for setting up a detection start point and a detection end point for an unregistered road on registered roads which are respectively located before and behind sections in which the matching result data from said road matching means indicates that the state of the identification is the free state, respectively, the matching result data indicating that the state of the identification is the matching state when the vehicle travels along each of the registered roads, for performing a coordinate transformation on a traveling path which is created on a basis of the positioning data from said positioning means and which is assumed to extend from said detection start point to said detection end point in a coordinate system so that a start point of the traveling path has coordinates which match with coordinates of said detection start point and an end point of the traveling path has coordinates which match with coordinates of said detection end point, and for detecting coordinates of the unregistered road from a portion of the coordinate-transformed traveling path which does not overlap any registered road; and a road data generating means for creating road data about the unregistered road on a basis of the coordinates of the unregistered road detected by said unregistered road detecting means, and for storing them in said road-map-data storage means.