A device and a method are provided in which stable tracking control can be carried out even in an arbitrary phase by optically reading pits provided in a disk when information is recorded on and reproduced from the disk with a magnetic head. With respect to difference signals obtained from a main beam signal and sub-beam signals obtained through three-beam type photodetectors, gain correction is executed in variable gain amplifiers, respectively, so that output signals therefrom have same amplitude levels and are different in phase by 90 degrees in a track crossing direction, and thus a tracking error signal is generated by being synthesized from the output signals. Based on the tracking error signal, tracking control is carried out.