PURPOSE: To obtain a tracking servo device which is not effected by the tilt, warp, etc. of a disk by using a signal generating means which performs comparisons among outputs of photodetecting elements and delivers and produces a tracking servo signal and also eliminating the offset voltage before a tracking servo action is started.

CONSTITUTION: If VA<A<VB is satisifed with the output voltage A of the 2nd differential amplifier 17, the reflected light given from a disk 10 is deviated toward the 2nd photodetecting element 13 owing to a tilt of the disk 10. Thus a control part 36 performs switching control among the 1stW6th switches SW1W SW6, and the 4th switch SW4 is turned on. Then the output amplification factor of the element 13 is controlled and set smaller than the output amplification factor of the 1st photodetecting element 12. The outputs of both elements 12 and 13 are compared with each other by the 1st differential amplifier 16 to obtain the subsequent tracking servo signals. Thus the offset voltage produced by the tilt of the disk 10 is eliminated. In such a way, the tilt of the disk 10 is decided by the level of the voltage A of the amplifier A. Based on the result of this decision, a difference of amplification factor is produced between the output of both elements 12 and 13. Then the offset voltage is eliminated to perform the subsequent tracking servo operations.