Abstract: A focus adjustment system for an optical disk apparatus has a monitor detector that detects the power of a light beam emitted from a laser, and a peak detector produces a peak-detect signal when peak beam power is detected. An optical system directs the light beam through an objective lens onto a disk, and feed light reflected from the disk back to the laser. A focus-error detector receives light reflected from the disk and produces a focus-error signal representing distance between the objective lens and the disk. A sample-and-hold circuit samples the focus-error signal when a peak-detect signal is produced, and outputs the sampled focus-error signal as a reference signal. A focus controller moves the objective lens toward or away from the disk according to the difference between the focus-error signal and the reference signal.