frequency amplifier 7 the rf amplifier 7 executes calculation processing of the information supplied thereto to extract a reproduction rf signal a tracking error signal a focusing error signal absolute position information information of an absolute position recorded as a pre group wobbling group on the magneto optical disc 1 address information sub code information a focus monitor signal and so forth the thus extracted reproduction rf signal is supplied to an encoder decoder section 8 meanwhile the tracking error signal and the focusing error signal are supplied to a servo circuit 9 and the address information is supplied to an address decoder 10 further the absolute position information and the focusing monitor signal are supplied to a system controller 11 which may be constituted for example from a microcomputer the servo circuit 9 generates various servo driving signals in response to the tracking error signal and the focusing error signal supplied thereto from the rf amplifier 7 and also to a track jumping instruction a seeking instruction rotational speed detection information and so forth supplied thereto from the system controller 11 to control the biaxial mechanism 4 and the thread mechanism 5 to effect focusing and tracking control and to control the spindle motor 2 to rotate at a constant angular velocity cav or a constant linear velocity clv the reproduction rf signal is processed by decoding processing.