A technology is provided whereby a lane can be correctly estimated without relying on lane markers. A shape indicating a road region is extracted from image data obtained by capturing images in the progression direction of a vehicle 6 and, on the basis of information indicating the shape, the angle of inclination for one contour line, the center-of-gravity coordinates for a diagram indicating the shape of the road region, the angle between two consecutive contour lines across one vertex of the diagram indicating the shape, and the area of the diagram indicating the shape are calculated as feature values for the shape of the road region. In addition, the lane in which the vehicle 6 is traveling can be estimated by determining whether or not the calculated feature values are included in a threshold value range preset for each lane.