1. A disparity calculation apparatus, comprising: a stereo image data acquisition section that acquires a target image in which an object is captured using a first imaging system, and a reference image in which the object is captured using a second imaging system; a stereo matching section that calculates a degree of difference of image brightness between a target point included in the target image and each of a plurality of search points, which are included in the reference image and corresponding to the target point; a corresponding point candidate number determination section that detects, from the search points, a search point for which the degree of difference of image brightness is minimal in a coordinate distribution of the search points, and if a plurality of the detected search points are present, determines each of the detected search points to be a corresponding point candidate; a corresponding point candidate detection section that detects each of a plurality of corresponding point candidates corresponding to a first target point as a first corresponding point candidate, and detects, for each of one or a plurality of second target points present in a peripheral area that includes the first target point, each of a plurality of corresponding point candidates, which are corresponding to the second target point and respectively corresponding to the first corresponding point candidates, as a second corresponding point candidate; a corresponding point determination section that calculates a first disparity value between the first target point and each of the first corresponding point candidates, calculates, for each of the one or plurality of second target points, a second disparity value between the second target point and each of the second corresponding point candidates, and determines a first corresponding point candidate for which variation is smallest among the first corresponding point candidates to be a corresponding point, the variation being variation between the first disparity value and the one or plurality of second disparity values corresponding to the first disparity value; and a disparity data output section that outputs disparity data, which is calculated based on a coordinate point of the corresponding point corresponding to the first target point and a coordinate point of the first target point.