Patent ID: 8036090

Claim:
An optical pickup device comprising: a laser light source; an irradiation optical system which condenses a laser light from the laser light source onto one recording layer of a multi-layer optical information storage medium; and a detection optical system which detects a reflected light reflected by the one recording layer of the multi-layer optical information storage medium, wherein: the detection optical system comprises: a light flux splitting optical system which parallel splits the reflected light from the one recording layer to both sides of an optical axis so that light fluxes obtained after parallel splitting the reflected light do not pass through the optical axis before reaching a condensing plane; a diffraction grating which is divided into a plurality of regions having different diffraction directions; a reflected light condensing lens which focuses the reflected light split by the light flux splitting optical system; and a detector which is provided on the condensing plane of the reflected light from the one recording layer, the reflected light being focused by the reflected light condensing lens; and a sensing region of the detector is provided in a region which is not irradiated with a reflected light from another recording layer different from the one recording layer.