1. A camera calibration apparatus comprising: an image obtaining section for obtaining a captured image including at least four indexes having a planar preferential calibration index arranged in a specified region and a planar non-preferential calibration index arranged in a non-specified region other than the specified region, the specified region and the non-specified region being defined in a first plane in a photographing view field of a camera; an index information storing section for determining the positional relationship between the preferential calibration index and the non-preferential calibration index in advance, and storing the coordinate positions of the preferential calibration index and the non-preferential calibration index in the first plane as actual coordinate positions; a preferential calibration index position calculating section for calculating the coordinate position of the preferential calibration index in the image; a non-preferential calibration index position calculating section for calculating the coordinate position of the non-preferential calibration index in the image by referring to the positional relationship and the calculated coordinate position of the preferential calibration index; a homography calculating section for calculating a homography between a captured-image surface of the captured image and the first plane based on the actual coordinate positions and the calculated coordinate positions of the calibration indexes representing the coordinates of at least four points; and a calibration section for performing calibration of the camera by using the homography, wherein the preferential calibration index is arranged in the specified region which is a near-side region having a short-range object distance from the camera, and the non-preferential calibration index is arranged in a far-side region having a long-range object distance from the camera.