Patent ID: 7787347

Claim:
An optical head device comprising: at least one light source; a collective lens for focusing a light emitted from the light source on an arbitrary recording layer of a multilayer optical disc including a plurality of recording layers; a light splitting element including a first light splitting element for splitting a reflected light from the arbitrary recording layer and a second light splitting element for splitting the reflected light split by the first light splitting element into at least three lights; and a photodetector comprising at least first to third light receiving regions, provided on one substrate, for detecting the at least three lights, wherein: the second light splitting element causes one of the at least three lights to be incident on the first light receiving region to detect an information signal from the optical disc, the second light receiving region is substantially arranged at a side of the focus position of the split light closer to the collective lens, the third light receiving region is substantially arranged at a position located at a side of the focus position of the split light opposite to the collective lens and symmetrical with the second light receiving region.