Focus searching method and optical disc device

摘要

A focus search driving voltage (R) corresponding to a signal surface (12) of an optical disc (10) is obtained on the basis of detection information (AS-cd) from a photodetector (65-70) when an objective lens (73) is focused on the signal surface (12) of the optical disc (10) in the middle of raising or lowering the objective lens (73) placed on standby at a lens midpoint between a temporarily set lens bottom point and a temporarily set lens top point according to a temporarily set lens bottom point voltage (±) and a temporarily set lens top point voltage (²). Then, a lens bottom point voltage (³) and a lens top point voltage (´) at the time of device starting are obtained by an arithmetic operation program based on the focus search driving voltage (R) and predetermined factors, and then a lens bottom point corresponding to the lens bottom point voltage (³) is set to be nearer to the lens midpoint side than the temporarily set lens bottom point while a lens top point corresponding to the lens top point voltage (´) is set to be nearer to the lens midpoint side than the temporarily set lens top point.