The present invention relates to calibration of camera parameters for converting a world coordinate system, which indicates a position in the real space, to a coordinate used in an image and vice versa. The apparatus according to the invention has a detection unit, which determines corresponding pixel pairs from the captured image and the model image and outputs corresponding data indicating determined pixel pairs, and a selection unit, which selects pixel pairs to be left in the corresponding data and removes data related to an unselected pixel pair from the corresponding data for generating selected corresponding data. The apparatus further has a calculation unit, which calculates camera parameters based on the selected corresponding data.