Focus servo device for detecting and compensating for disk abnormalities

In an apparatus for reproducing recorded information, including a pickup for reproducing information recorded on a recorded disk, and a tracking servo device for maintaining said pickup within a recorded track on said disk, a focus servo device in which a spotlight irradiated from said pickup is controlled in accordance with a focus error signal so as to correctly converge said spotlight on a recording surface of said disk, whrein said pickup includes a single recorded-information detecting spotlight and a pair of tracking information detecting spotlights respectively preceding and succeeding said single recorded-information detecting spotlight when said recorded-informating detecting spotlight moves relative to said recording disk, said focus servo device comprising abnormality detecting means for detecting abnormalities on said recording surface in accordance with a level of output signals of said preceding tracking information detecting spotlight, wherein said abnormality detecting means holds a detected abnormality output for a predetermined time after disappearance of said output signals, and gain setting means for setting a gain of a servo loop, said gain setting means reducing the loop gain in a predetermined frequency band within a servo zone in response to said detected abnormality output from said abnormality detecting means, said focus servo device prevening said abnormalities from affecting said tracking servo device.