Optical disk apparatus, focal position control method and focal position control apparatus

Abstract

An optical disk apparatus can reliably detect the target recording layer of an optical disk having two recording layers. The optical disk apparatus is adapted to recording information on and reproducing information from an optical disk formed by sequentially laying a first recording layer, a second recording layer and a cover layer. The focal point of the light beam is moved closer to the optical disk from the side of the cover layer and the focal point of the light beam is determined to be coming close to the recording layer when the signal level of the focus error signal falls below a positive focus error threshold value after rising above the latter or rises above the negative focus error threshold value after falling below the latter. Then, the focal point of the light beam is kept on moving toward the optical disk after the detection of the recording layer and the recording layer that is detected last is determined to be the first recording layer when the recording layer is not re-detected within a re-detection period.