A stereo camera implements ranging of an object that includes consecutive similar patterns. In stereo matching using the stereo camera, if a plurality of corresponding point candidates are present in a sum of absolute differences (SAD) or suchlike evaluation value distribution for a target point, an evaluation value map is generated by superimposing an evaluation value distribution of a target point for which a plurality of corresponding points are determined to be present and an evaluation value distribution of each other target point present in a peripheral area of that target point. By this means, the shape of an object is represented in real space around a target point for which a plurality of corresponding points are determined to be present, and it is possible to calculate the true distance of a railing or the like that extends in a straight line by extracting a line segment with the strongest linearity in the evaluation value map.