PURPOSE: To provide the optical position detector with which information expressing characters or graphics written on a tablet can be immediately obtained.

CONSTITUTION: This device is composed of a tablet 1, writing object 3 equipped with a light reflection plane 3 and position detector 2 fitted onto the tablet 1 so as to detect the position of the writing object 3 on the tablet 1 with light, and the position detector 2 is provided with a polygon mirror 7 to be rotated, a pair of light sources 9 and 10 for projecting light onto the polygon mirror 7, a pair of light receiving elements 11 and 12 for receiving the reflected light of the polygon mirror 7 or the writing object 3 and outputting detecting signals, reference light receiving element 13 for receiving the reflected light of the polygon mirror 7 and outputting a synchronizing signal, arithmetic part for performing various kinds of arithmetic, and control part for controlling respective parts. Based on the output time difference of respective detecting signals from the synchronizing signal, the incident/exit angle of light made incident on the writing object 3 on the reflection plane of the polygon mirror 7 is calculated, and the rectangular coordinate position of the writing object 3 on the tablet 1 is detected by prescribed arithmetic using the incident/exit angle.