PURPOSE: To accurately judge a focus abnormality or the other abnormality at the time of the occurrence of an abnormal state by providing a focus abnormality detector.
CONSTITUTION: The distance (focus error) between the focus of laser light passing an objective lens and a disk is detected to lead the focus onto the disk surface. A means is provided which discriminates excess of the focus error detection signal over a prescribed value to output a signal indicating the focus abnormality. That is, the focus abnormality is discriminated if a large deviation of the focus of laser light from the disk surface occurs which cannot occur in the normal focus servo state, and the focus abnormality is detected from the focus error signal. Thus, the focus servo leading-in operation is not performed unless the focus abnormality occurs in the case of the occurrence of the abnormal state, and this operation is performed when the focus abnormality occurs.