An image segmenting unit (401) in the stereo image processing device (100) extracts M (a natural number between 2 and N, inclusive) number of segmented target images wherein a first partial area within a target image has been segmented into N (a natural number of 2 or more), and also extracts M number of segmented reference images wherein a second partial area within a reference image has been segmented into N. An image concatenating unit (402) serially concatenates M data strings, each comprising a intensity value from each segmented target image, to form a first image data string and also serially concatenates M data strings, each comprising a intensity value from each segmented reference image, to form a second image data string. A filtering unit (403) and a peak position detection unit (104) calculate the disparity between the standard images and the reference images.