Abstract: In a small-sized optical pickup device for enabling to obtain a stable servo-signal, as well as, a focus error signal and a tracking error signal, without receiving ill influences of stray lights from other layers, when recording/reproducing a multi-layer optical disc, a reflection light from the multi-layer optical disc is divided into plural numbers of regions by a diffraction grating. And, it is divided into at least four (4) regions, by a division line in the tangential direction of the optical disc and a division line in the radial direction thereof. Light receiving parts, for detecting either one of grating diffraction lights, i.e.