Wobble detection circuit corresponding to a plurality of media having different pre-formats and optical disk apparatus having reduced size

摘要

A wobble detection circuit detects a signal by a common photodetector (light receiving) element from several kinds of media having different pre-formats. Further, the wobble detection circuit changes a gain for amplifying the signal in a wobble signal detection process depending on the pre-format of a reproducing or recording medium to obtain a wobble signal.