1. A stereo ranging apparatus that calculates the distance to a target using a first image and a second image of the target, the apparatus comprising a processor having one or more integrated circuits configured to: store blur adjusting filter coefficients corresponding to combinations of image heights of the first image and image heights of the second image; compare an image height of a first partial image which is an image of the target in the first image and an image height of a second partial image which is a candidate for an image of the target in the second image; acquire a blur adjusting filter coefficient that corresponds to a combination of the image height of the first partial image and the image height of the second partial image from the filter storage section; adjust the blur of one partial image with the lower image height of the first partial image and the second partial image to the blur of the other partial image with the higher image height, using the acquired blur adjusting filter coefficient; determine whether the second partial image is the image of the target in the second image based on the partial image with the adjusted blur and the partial image with the unadjusted blur; measure disparity between the first partial image and the second partial image when the second partial image is the image of the target in the second image; and calculate the distance to the target based on the disparity.