Patent ID: 8111602

Claim:
An objective lens for use in an optical pickup apparatus, for forming a converged spot on an information recording surface of a first optical disc including a protective layer with a thickness t1 by using a first light flux with a wavelength λ1 (μm) emitted from a first light source, and for forming a converged spot on an information recording surface of a third optical disc including a protective layer with a thickness t3 (t1<t3) by using a third light flux with a wavelength λ3 (1.7λ1<λ3<2.3λ1) emitted from a third light source, wherein an optical surface of the objective lens comprises a first basic structure being an optical path difference providing structure, the first basic structure comprises a step structure in which a plurality of ring-shaped step units are arranged concentrically about an optical axis as a center, and a step-difference amount d1 of a small step difference in each of the step units, in a direction of the optical axis satisfies the following conditional expression, where n is a refractive index of the objective lens for the first light flux: 0.5λ1/( n− 1)< d 1<λ1/( n− 1) (1).