A stereo image processing apparatus adapted to compute a subpixel-level disparity between a target image and a reference image that form stereo images, the stereo image processing apparatus comprising: an extraction section adapted to extract a first unit partial target image for subpixel estimation from the target image by applying a first window function at an extraction target position, and to extract a first unit partial reference image for subpixel estimation from the reference image by applying the first window function; a computation section adapted to compute a first subpixel-level disparity based on a phase difference between a data sequence including intensity values of the extracted first unit partial target image for subpixel estimation and a data sequence including intensity values of the extracted first unit partial reference image for subpixel estimation; a window function setting section adapted to set, with respect to the extraction section, a second window function, which is formed by shifting the first window function by an amount corresponding to the first subpixel-level disparity computed by the computation section, the second window function being different from the first window function; a second extraction section adapted to extract a second unit partial target image for subpixel estimation from the target image by applying the first window function at an extraction target position, and to extract a second unit partial reference image for subpixel estimation from the reference image by applying the second window function; and a second computation section adapted to compute a second subpixel-level disparity based on a phase difference between a data sequence including intensity values of the extracted second unit partial target image for subpixel estimation and a data sequence including intensity values of the extracted second unit partial reference image for subpixel estimation. an extraction section adapted to extract a first unit partial target image for subpixel estimation from the target image by applying a first window function at an extraction target position, and to extract a first unit partial reference image for subpixel estimation from the reference image by applying the first window function; a computation section adapted to compute a first subpixel-level disparity based on a phase difference between a data sequence including intensity values of the extracted first unit partial target image for subpixel estimation and a data sequence including intensity values of the extracted first unit partial reference image for subpixel estimation; a window function setting section adapted to set, with respect to the extraction section, a second window function, which is formed by shifting the first window function by an amount corresponding to the first subpixel-level disparity computed by the computation section, the second window function being different from the first window function; a second extraction section adapted to extract a second unit partial target image for subpixel estimation from the target image by applying the first window function at an extraction target position, and to extract a second unit partial reference image for subpixel estimation from the reference image by applying the second window function; and a second computation section adapted to compute a second subpixel-level disparity based on a phase difference between a data sequence including intensity values of the extracted second unit partial target image for subpixel estimation and a data sequence including intensity values of the extracted second unit partial reference image for subpixel estimation.