PURPOSE: To cope with even large vertical shake by detecting the angle of incidence of a light beam on an optical disk and inclining a spindle in such direction that the angle of incidence is 90°.

CONSTITUTION: A tracking servo circuit 16 operates the difference signal between signals outputted from two photodetectors 12a and 12b to output a servo signal proportional to the extent of deviation of the tracking position. Consequently, a spindle 1 is inclined by an inclining motor 6 in such direction that a laser beam 7 is made perpendicularly incident on the signal face of an optical disk 3. When the laser beam 7 is made perpendicularly incident on the signal face of the optical disk 3, the signal face of the optical disk 3 is placed in an about center of the servo range of a tracking servo circuit 16, and the optical axis of the laser beam 7 coincides with a recording track to correct the tracking deviation. Thus, the burden of a servo system is reduced to record/reproduce normal information.