Patent ID: 7023777

Claim:
An optical disc recording/reproducing apparatus, comprising: recording/reproducing means for recording/reproducing information by emitting a light beam onto a disc having a track which wobbles at a predetermined frequency; reflected light detection means for detecting the light beam reflected from the disc; wobble signal detection means for detecting a wobble amplitude signal which represents an amplitude of a signal generated from a component which is extracted from an output of the reflected light detection means and which wobbles at the predetermined frequency; a low pass filter control section for passing a low band component of the wobble amplitude signal; and variation rate detection means for detecting dirt adhered on the disc, wherein the low pass filter control section has a passage characteristic which does not pass a variation frequency component caused due to the dirt but passes a rotation frequency component of the disc, and the variation rate detection means detects a variation rate by calculating a ratio of an output of the low pass filter control section to the wobble amplitude signal, thereby detecting the dirt based on the output of the low pass filter control section and the wobble amplitude signal before the recording/reproducing means records/reproduces the information.