A photosensor receives laser light reflected from an optical disk with a two-segmented photodetecting surface. A relative speed detecting section binarizes a difference signal of output signals of the photosensor, and detects time points when the laser light is located at the centers of tracks and grooves of the optical disk. When a detected interval is longer than a preset value, the relative speed detecting section outputs a speed detection pulse having a preset pulse width. A track detecting section binarizes a sum signal of the output signals of the photosensor, detects time points when the laser light is located at a track edge, and outputs a track detection pulse having a preset pulse width. A loop switch turns on/off a tracking servo loop in accordance with a tracking start signal that is generated by an AND circuit and a D flip-flop.