Patent ID: 8189434

Claim:
An optical pickup unit comprising: a splitting section for at least (i) splitting at least one tracking-use main beam from a main beam which has been reflected off a storage medium and passed through a converging section and (ii) splitting at least one tracking-use sub beam from each of sub beams having lower light intensity than the main beam, the tracking-use main beam and the tracking-use sub beam used for determining a tracking servo signal, the storage section including plural information writing layers being laminated; and a light-receiving section for receiving the tracking-use main beam and the tracking-use sub beam, the light-receiving section including: (A) at least one tracking-use main light-receiving region for receiving the tracking-use main beam, (B) tracking-use sub light-receiving regions each for receiving the tracking-use sub beam, and (C) auxiliary light-receiving regions each for receiving only a light beam reflected off an information writing layer other than the information writing layer subjected to an information reading/writing process, each of the auxiliary light-receiving regions serving as a light-receiving region for use in error amount calculation for restraining an error in the tracking servo signal, and each of the auxiliary light-receiving regions having a smaller light-receiving area than that of each of the tracking-use sub light-receiving regions, wherein in a case where a gain is added to a signal output based on a light quantity in the light-receiving section, a gain added to a signal derived from the auxiliary light-receiving regions is equal to a gain added to a signal derived from the tracking-use sub light-receiving regions.