A calibration apparatus is configured to acquire calibration data indicating a correspondence between two-dimensional pixel coordinates of the image-conversion device and three-dimensional world coordinates of the world coordinate space and calculate parameters by fitting, to the acquired data, a camera model in which two coordinate values of the two-dimensional pixel coordinates are expressed as a function of three coordinate values of the three-dimensional world coordinates. When a projection relationship between an angle of view and an image height of the optical system is roughly expressed by a predetermined expression by using a projection focal distance, the apparatus is configured to convert three-dimensional world coordinates of the acquired data to two-dimensional coordinates and, subsequently, by fitting a camera model in which the two coordinate values of the two-dimensional pixel coordinates are expressed as a function of two coordinate values of the two-dimensional coordinates, calculate the parameters of the camera model.