In a correlation process between image patterns seen by two stereo-viewing cameras, the process can be made faster by using only the information related to a coordinate in the direction having a parallax, concerning the position of a characteristic point in the image patterns. In addition, by introducing a process for verifying the positional information of the characteristic point obtained by a camera for verification, it is possible to suppress a decrease in the characteristic information contained in the image patterns and to improve the precision of the correlation process. As a result, it is possible to achieve a stereo image processing device which operates at high speed. Further, since the stereo image processing device can be realized by a comparatively simple circuit configuration, it is expected that the device can contribute to the commercialization of in-vehicle safety monitor devices and the like.