PROBLEM TO BE SOLVED: To provide an optical pickup defocus error signal detector, a seek method detector and its method adopting the detector. SOLUTION: This invention provides the optical pickup defocus error signal detector that generates 1st-3rd detection signals by dividing a light into 1st-3rd optical regions in directions corresponding to radial directions of a recording medium and detects a defocus error signal through the subtraction between the 2nd detection signal and a sum signal of the 1st and 3rd detection signals. Furthermore, this invention provides the seek direction detector and method that is configured to detect a seek direction of the recording medium adopting a land/groove structure by comparing the detected defocus error signal with a push-pull tracking error signal. Since the detected defocus error signal is not susceptible to a relative tilt of a recording medium with respect to an objective lens, a de-track, and a shift of the objective lens or the like, using this defocus error signal can accurately control the defocus and detect a change in the thickness of the recording medium.
OPTICAL PICKUP DEFOCUS ERROR SIGNAL DETECTOR AND METHOD, AND SEEK METHOD DETECTOR AND METHOD ADOPTING THEM