a coordinate input apparatus includes a coordinate input member for inputting the coordinate value of an indicated position by pointing to a desired position with an indicating pen , a display device for displaying in dot form the indicated position of the indicating pen on the coordinate input member , an instruction device for instructing a calibration process for matching the coordinate systems of the coordinate input member and the display device , a correction parameter derivation device for deriving a correction parameter for matching coordinate systems on the basis of the indication by the indicating pen to a specific region of the coordinate input member when the instruction device has instructed , a coordinate value derivation device for deriving the coordinate value of the indicated position of the indicating pen to the specific region by using the correction parameter derived by the correction parameter derivation device , and a judgment device for judging the validity of the correction parameter according to whether or not the coordinate value derived by the coordinate value derivation device belongs to the specific region .