OPTICAL DIGITIZER WITH FUNCTION TO RECOGNIZE KINDS OF POINTING INSTRUMENTS

An optical digitizer which has a function to recognize kinds of pointing instruments, allowing an input by a finger or by a pen, is provided. The optical digitizer includes: a light source to emit a light ray; an image taking device which is arranged in a periphery of a coordinate plane, and which converts an image of the pointing instrument into an electrical signal after taking an image of the pointing instrument by using the light ray of the light source; a computing device to compute the pointing position coordinates after processing the converted electrical signal by the image taking device; a polarizing device to polarize the light ray emitted by the light source into a first polarized light ray or a second polarized light ray; a switching device to switch the irradiating light on the coordinate plane to the first polarized light or the second polarized light; a retroreflective material with retroreflective characteristics, which is installed at a frame of the coordinate plane; a polarizing film with a transmitting axis which causes the first polarized light ray to be transmitted; and a judging device to judge the pointing instrument as the first pointing instrument when the image of the pointing instrument is taken by the first polarized light ray, and to judge the pointing instrument as the second pointing instrument when the image of the pointing instrument is taken by the second polarized light ray.