Patent ID: 7768882

Claim:
A focal control adjusting method comprising: a first step for detecting a focal error signal obtained through condensing and irradiating a light beam on a rotating recording medium; and a second step for setting a focal control gain for controlling a positional shift between a recording surface of the recording medium and the light beam based on the focal error signal detected in the first step, wherein: three beam condensing spots are formed on the rotating recording medium through condensing and irradiating the light beam consisting of a main light beam and two sub light beams on the recording medium, a first position detection signal indicating a position of the beam condensing spot in the main light beam is generated based on a main reflected light obtained through reflection of the main light beam on the recording medium, and second position detection signals indicating positions of the beam condensing spots in the sub light beams are generated based on two sub reflected lights that are reflected on the recording medium and have phases different from that of the main reflected light in the first step, a result obtained by multiplying the second position detection signal by a preset coefficient is added to the first position detection signal, and a result of the addition is detected as the focal error signal in the first step, the coefficient is set in accordance with the focal error signal in the first step, the focal control gain is set in accordance with the focal error signal, the first position detection signal or the second position detection signals in the second step, and the focal control gain is applied only when a tracking control loop for controlling the positional shift between the track of the recording medium and the light beam is open in focal adjustment of the light beam based on the focal error signal detected in the first step and the focal control gain set in the second step.