Focusing control apparatus, recording medium, and optical disk playaback appatatus

A program which can be run by an entertainment apparatus which comprising:

• an object lens which condenses a light beam on an optical disk constructed of a plurality of signal recording layers;
• focusing drive means for moving said object lens in a direction orthogonal to the recording layers of the optical disk;
• photodetection means for detecting light reflected from said optical disk;
• and
• focus error signal generation means for generating a focus error signal which corresponds to defocusing of said object lens relative to a specified one of said recording layers of said optical disk, on the basis of a detection signal of said photodetection means;
• wherein said program causes the entertainment apparatus to execute:
• a peak detection process for detecting peaks of the focus error signal;
• a reference value calculation process for calculating reference values of said focus error signal in accordance with detection signals of said peak detection process;
• a comparison signal generation process for comparing said focus error signal with its reference values, and generating comparison signals based on results of the comparisons;
• and
• a process for accepting a request for moving a focusing position of said object lens, and generating and outputting signals which control said focusing drive means, on the basis of the detection signals of said peak detection means and the comparison signals.