1. A calibration apparatus comprising: a distance image generation section that calculates a distance from a stereo camera for each of a plurality of pixels included in a stereo image and that generates a distance image in which each of the plurality of pixels is associated with the calculated distance; a first region detection section that detects a road surface image region based on the stereo image; a second region detection section that detects a setting prohibited region including a group of non-effective pixels with which calculating the distance in the distance image is not possible; an area setting processing section that adjusts an arrangement pattern in a direction in which a plurality of area setting frames become distant from each other, based on the road surface image region and the setting prohibited region; an extraction processing section that extracts, from the distance image, a plurality of partial images corresponding to the plurality of area setting frames included in the adjusted arrangement pattern; and a calculation section that calculates an installation state parameter regarding an installation state of the stereo camera used for capturing of the stereo image, based on the plurality of extracted partial images.