PURPOSE: To obtain a tracking servo device whose circuit constitution is simplified by a one-spot push-pull system, which enhances the utilizing efficiency of a laser and enables it to comply with a separation type optical system'.

CONSTITUTION: A prelens 12 condensing light from an infinite magnification lens 10 is arranged in front of an MDP 11 and wobbled by a driving signal from a wobbling driving part 13. Then, a push-pull signal and an offset-canceled position signal are outputted by an offset extraction part 14 based on output from received light quantity obtained by detecting the light returned from the infinite-magnification objective lens 10 by the respective photodetectors 11P and 11S of the MPD 11.