To reduce the burdens of the operator of the calibration work of a transparent digitizer.

When the operator performs pointing with a dedicated pen 10 at a first reference point displayed on a screen 12 and then performs pointing with the dedicated pen 10 at a second reference point displayed on the screen 12, a personal computer 17 automatically generates transformation information such as a 'shift amount' and a 'magnification' and informs the transparent digitizer 13 of it. Thus, the transparent digitizer is easily calibrated.