1. A disparity value deriving device for deriving a disparity value representing disparity for an object from a first reference image obtained by a first imaging unit for imaging the object and a first comparison image obtained by a second imaging unit for imaging the object, the second imaging unit being located at a different position from the first imaging unit, the disparity value deriving device comprising: a reducer configured to generate a second reference image and a second comparison image by reducing the first reference image and the first comparison image, respectively, by a first ratio; a calculator configured to calculate degrees of matching of a plurality of regions in a predetermined range in the second comparison image with a first reference region in the second reference image, the predetermined range including a corresponding region that corresponds to the first reference region; a synthesizer configured to obtain a synthesis degree of matching for each of the regions by aggregating the degrees of matching in the second comparison image for a second reference region located in neighborhood of the first reference region, with the degree of matching of the regions; a deriving unit configured to derive the disparity value between the first reference region and the corresponding region, based on the synthesis degrees of matching; a generator configured to generate a first disparity image based on disparity values derived by the deriving unit; and an enlarging unit configured to enlarge the first disparity image by a second ratio to generate a second disparity image, by placing at least one first correction pixel between referential pixels that are consecutive in column and row directions and by placing a second correction pixel in a space generated between consecutive ones of the first correction pixels, the referential pixels being pixels included in the first disparity image.