In an optical disk apparatus, for reproducing information recorded on a recording surface of an optical disk, by setting such a focus condition that a tracking servo-error level comes to be maximum with a reflection light from the recording surface, while irradiating a light beam of a semiconductor laser, within a signal processor portion 300 for amplifying a RF signal reproduced from the optical disk is provided an equalizer 330 for lifting up high-frequency region of the RF signal, wherein an optimal control is made on an amount of lifting (i.e., EQ Boost Value) by the equalizer, depending upon a difference (.DELTA.AF) between a focus offset amount at which the RF signal reproduced comes to be maximum and a focus offset amount at which jitter of the RF signal reproduced come to be minimum.