Patent ID: 7835241

Claim:
An optical disc playback apparatus for playing back an optical disc, comprising: a light emitting unit configured to irradiate said optical disc with light; a light condensing unit configured to condense reflected light from said optical disc; a driving unit configured to drive said light condensing unit in a focusing direction; a calculating circuit configured to calculate strength of a signal based on said reflected light condensed by said light condensing unit; a first detecting circuit configured to detect a first change in said strength; a second detecting circuit configured to detect a second change in said strength after said first change is detected; a playback unit configured to play back said optical disc when said second change is detected within a predetermined time; and a stopping circuit configured to stop said driving unit when said second change is not detected within said predetermined time, wherein said predetermined time is defined in accordance with a distance between said light condensing unit and a surface of said optical disc when said first change is detected, and with moving speed of said light condensing unit.