To provide a map data automatic updating system for writing road data to map data when an own car drive a road that is not listed on the map data.

The automatic updating system comprises a camera 4 for imaging the surrounding image of a vehicle, an own car position detection section 11 for detecting the position of the own car, a road recognition section for extracting a white line from an image that is imaged by the camera 4 and for judging whether a road is present or not at the driving position of the car, and a road data-writing-section for judging whether the road is present or not on the map data when the road is detected by the road recognition section and for performing writing processing where the road is written into the map data as new road data when the road is not present in the map data.