PURPOSE: To accurately detect abnormality in a focus servo and to prevent the flowing of excess current in the focus coil even when the optical pick-up is moved in any direction.

CONSTITUTION: The responding light in a luminous flux with which optical card 1 is irradiated is converted into an electric signal by an optical detector 7. A demodulation circuit 16 converts each electric signal obtained from the light receiving surface divided into plural in the optical detector 7 into each regenerative signal. Then, a control circuit 41 inputs the preliminary set reference value in a comparator 43 and makes this comparator compare with the each regenerative signal by the reference value. If at least one of the regenerative signals is higher than the reference value, it is decided that the focusing control state by the focus servo is normal.