An optical information processor including a recording medium with a guide groove having interrupting portions therealong in the form of mirror areas for reflecting light impinging on the recording medium. A light detector is provided for receiving diffraction light from the guide groove with a first signal detector being provided for differentially operating on signals from the light detector and generating a tracking signal tracking the guide groove. Additionally, a second signal detector is provided for detecting the signal from the light detector indicative of the mirror areas and providing an output indicative thereof which is utilized for compensating the tracking signal. The compensated tracking signal is then utilized for controlling the positioning of the light beam on the recording medium.