Patent ID: 6842408

Claim:
An optical disk apparatus for recording and reproducing data on and from an optical disk having a signal-recording surface, said apparatus comprising: optical head means for applying a light spot to the signal-recording surface of the optical disk; focusing control means for controlling the focusing operation the optical head means performs to place the signal-recording surface of the optical disk within a focal distance of the light spot applied by the optical head means; evaluation-function generating means for generating an evaluation function for correcting a focus value set in the focusing control means, in accordance with signals the optical head means has generated from light reflected from the optical disk; and control means for setting an initial focus value at a point where the evaluation function generated by the evaluation-function generating means is minimal or maximal, for setting an observation point deviating from the point where the initial focus value is set, and for correcting the initial focus value in accordance with changes in the evaluation function at the observation point.