Patent ID: 8467282

Claim:
An optical disc device for recording or reproducing information with respect to an information recording medium having three or more information recording surfaces with light transmissive layers of different thicknesses from each other, the optical disc device comprising: a light source which emits laser light; an objective lens which converges the laser light emitted from the light source on a predetermined one of the information recording surfaces of the information recording medium; a spherical aberration correcting section which corrects a spherical aberration resulting from the thickness of the respective light transmissive layers of the information recording medium; a lens tilting section which tilts the objective lens in a radial direction of the information recording medium; and a tilt detecting section which detects a tilt of the information recording medium in the radial direction, wherein assuming that an aberration amount of third-order coma aberration resulting from tilting the information recording medium by a unit angle is CMD0 (unit: mλ/deg), an aberration amount of third-order coma aberration resulting from tilting the objective lens by a unit angle is CML0 (unit: mλ/deg), a tilt angle of the information recording medium detected by the tilt detecting section is 0, a coefficient is k0, and a tilt angle of the objective lens by the objective lens tilting section is α 0 in converging the laser light on an information recording surface L0 having a largest light transmissive layer thickness out of the information recording surfaces of the information recording medium, the lens tilting section tilts the objective lens in such a manner that the tilt angle α 0 of the objective lens satisfies the mathematical expression (1): α0=θ× k 0 ×CMD 0 /CML 0, where 0.5<k0<0.9 (1).