1. An object detecting device that detects an object on a road surface included in stereo images, comprising: a disparity map generator that generates a disparity map on the basis of the stereo images; a road surface estimator that estimates a road surface region on the basis of the disparity map; an object candidate location extractor that extracts pieces of disparity data above the road surface region from the disparity map, as an object candidate region where an object candidate is present; an object identifying region extractor that extracts an object identifying region from the disparity map, the object identifying region including the object candidate region and having a width larger than the width of the object candidate region by a predetermined scale factor; a geometric feature extractor that extracts a geometric feature in the object identifying region; and an object identifying unit that identifies whether the object candidate is an object or a road surface on the basis of the geometric feature.