A road shape estimating device has a data obtaining processing unit for obtaining interpolation point data for a plurality of shape interpolation points which are set along a road and represent a shape of the road, a radius calculation processing unit for calculating a radius of curvature at each of the shape interpolation points based on the interpolation point data for a predetermined section of the road, a corner detection processing unit for detecting a corner in the predetermined section based on the radii of curvature, and a corner dividing processing unit for dividing the corner at a shape interpolation point having a radius of curvature equal to or larger than a threshold in the detected corner. The threshold is set corresponding to an average value of radii of curvature at respective shape interpolation points in the detected corner.