7 2 in fig6 b indicates close seek in which the optical pickup unit 7 is driven at a constant speed based on the period of the tracking error signal and 3 in fig6 b indicates track jump in which acceleration and deceleration voltages are applied to the tracking actuator to move the focal spot to a nearby track it is preferable that the spherical aberrations correction position be changed using 1 coarse seek together in order not to be affected by the degradation of the tracking error signal due to optical axis shift of the spherical aberrations correction lens 5 during coarse seek the present embodiment when the spot reaches a change position during reading drives the aberrations correction motor 6 to change the spherical aberrations correction position while continuing read operation but the present invention is not limited specifically it would be possible that the spherical aberrations correction position for a relevant zone is changed when amplitude reduction of the read signal is detected it would also be possible that the spherical aberrations correction position for a relevant zone is changed if a data read error or address read error occurs the present embodiment calculates information about the radius position of the disc currently irradiated with a focal spot from a physical address of the disc but the present invention is not limited thereto specifically it would be possible that the radius information detecting unit 21 detects radius information from the moving distance of the seek motor for example when the seek motor is a stepping motor a radius position of the disc can be calculated with the number of drive steps from the reference position with reference.