A stereo-image processing apparatus includes a stereo-image taking means configured to take a plurality of images from different viewpoints, a parallax detecting means configured to detect a parallax of a subject on the basis of the images taken by the stereo-image taking means, an object detecting means configured to detect objects on the basis of the parallax detected by the parallax detecting means and a parallax offset value, and a parallax-offset-value correcting means configured to correct the parallax offset value on the basis of a change in a parallax corresponding to an object whose size in real space does not change with time, of the objects detected by the object detecting means, and a change in an apparent size of the object.