1. A disparity deriving apparatus for deriving disparity of an object based on a reference image of the object captured at a first image capturing position and a comparison image of the object captured at a second image capturing position, the disparity deriving apparatus comprising: processing circuitry configured to calculate costs between a first reference area in the reference image and each one of corresponding areas corresponding to the first reference area in a given region in the comparison image, and costs between a second reference area, surrounding the first reference area in the reference image, and each one of corresponding areas corresponding to the second reference area in a given region in the comparison image; synthesize the costs of the first reference area, and the costs of the second reference area as synthesis costs; derive a disparity value of the object captured in the first reference area based on the synthesized synthesis costs; and apply a spatial filter to a local region, composed of a plurality of areas, each area of the plurality of areas having a corresponding disparity value, in the first reference area to correct a specific disparity value in the local region by changing the specific disparity value in the local region to a new value using the spatial filter, wherein, in applying the spatial filter to the disparity values of the local region, excluding a disparity value of one area of the local region having low reliability from the application of the spatial filter.