a processor configured to apply a Hough transform to coordinate points on a U-disparity (UD) map, each coordinate point of the coordinate points on the UD map having two-dimensional coordinates formed by a first direction corresponding to a horizontal direction of a captured image generated by a stereo camera capturing an image of a road surface and a second direction corresponding to a magnitude of a disparity among disparities acquired from the captured image, the UD map associating a target disparity among the disparities satisfying a predetermined condition with target coordinate points of the coordinate points to detect a straight line having a predetermined length, and to detect the target disparity corresponding to the detected straight line having the predetermined length as a disparity corresponding to an object parallel to a direction of travel of the stereo camera, wherein

the processor is configured to convert, in the Hough transform, a straight line passing through the target coordinate points associated with the target disparity and a predetermined range based on a vanishing point into a Hough space, and

the processor is configured to exclude, from the application of the Hough transform, coordinate points on the UD map for which magnitudes of disparities are substantially identical, and whose coordinates of the two-dimensional coordinates formed by the first direction are continuous in a predetermined range among the coordinate points on the UD map.