1. A road learning device comprising: a map data storage device that stores map data; an own vehicle location detection portion that detects a location of an own vehicle; a travel data storage device that stores travel data including the location of the own vehicle; an unregistered road travelling determination device that determines whether the own vehicle is travelling on a registered road indicated by the map data stored in the map data storage device or an unregistered road not indicated by the map data; an unregistered road travel data storage control device that controls the travel data storage device to store a group of the travel data of the unregistered road as a group of unregistered road travel data when the unregistered road travelling determination device determines that the own vehicle travels the unregistered road; a potential unregistered road track creation device that creates a travelled track of the unregistered road from the group of the unregistered road travel data stored in the travel data storage device as a potential unregistered road track; a first correction device that corrects the potential unregistered road track in a predetermined first correction manner so as to be a first track in order to merge the potential unregistered road track with the map data of the registered road; a map-matching trial device that successively applies map-matching of the unregistered road travel data to the first track; a primary successful map-matching determination device that determines whether the map-matching of the group of the unregistered road travel data to the first track is successful after the map-matching trial device executes a trial; a second correction device that corrects the first track in a second correction manner different from the first correction manner so as to be a second track when the primary successful map-matching determination device determines that the map-matching is unsuccessful; a secondary successful map-matching determination device that controls the map-matching trial device to execute the trial on the second track, and determines whether the map-matching of the group of the unregistered road travel data to the second track is successful; and a new map data storage control device that discards the group of the unregistered road travel data when the secondary successful map-matching determination device determines that the map-matching is unsuccessful, controls the map data storage device to store the first track by merging the first track with the map data of the registered road when the primary successful map-matching determination device determines that the map-matching is successful, and controls the map data storage device to store the second track by merging the second track with the map data of the registered road when the secondary successful map-matching determination device determines that the map-matching is successful.