Patent ID: 7995430

Claim:
An optical disk device for focusing a laser beam onto an optical disk using an objective lens and reproducing data recorded on the optical disk as a string of recording marks of different lengths, based on the laser beam reflected from the optical disk, comprising: a detection unit for detecting a position of the objective lens where the amplitude of the reproduction signal during the period corresponding to a minimum-length recording mark and a space having the same length reaches its maximum; and a setting unit for setting the detected position as a reference position for the objective lens relative to the optical disk, for use in focus control; wherein the detection unit reproduces test data recorded on the optical disk while sequentially hanging the position of the objective lens relative to the optical disk, detects, at each position, the amplitude of the reproduction signal during the period corresponding to a minimum-length recording mark and a space having the same length; and detects, based on the detection result, the position of the objective lens where the amplitude of the reproduction signal during the period corresponding to a minimum-length recording mark and a space having the same length reaches its maximum.