A stereo image processing apparatus is provided. The apparatus comprises an imaging device for taking a pair of images of an object for stereo image processing purpose; a stereo processor for correlating the pair of images for each small area thereof to thereby perform stereo matching processing for identifying corresponding areas, and obtaining an evaluation function as a result of said stereo matching processing, distance information to said object obtained based on said evaluation function, and reliability information indicating a reliability of said distance information; a parallax corrector for setting an adaptive search range around a small area in question according to said reliability information, obtaining a corrected evaluation function by correcting said evaluation function obtained for said small area in question based on said evaluation function obtained for a respective small area within said adaptive search range, and correcting said distance information based on said corrected evaluation function obtained.