Patent ID: 8385181

Claim:
An objective lens for an optical pickup apparatus comprising an objective lens for forming a converged spot on an information recording surface of a first optical disc including a protective layer with a thickness t 1 by using a first light flux with a wavelength λ 1 emitted from a first light source, for forming a converged spot on an information recording surface of a second optical disc including a protective layer with a thickness t 2 (t 1 ≦t 2 ) by using a second light flux with a wavelength λ 2 (λ 1 <λ 2 ) emitted from a second 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 t 3 (t 2 <t 3 ) by using a third light flux with a wavelength λ 3 (λ 2 <λ 3 ) emitted from a third light source, the objective lens comprising an optical surface comprising a first optical path difference providing structure which is a step structure in which a plurality of ring-shaped step units each including same number of steps are arranged concentrically about an optical axis as a center, wherein a width w 1 which is a width in a perpendicular direction to the optical axis of one of a highest step and a lowest step of at least one of the step units, and an average value w 2 which is an average of widths of two steps arranged at both sides of the one of the highest step and the lowest step along a direction perpendicular to the optical axis satisfy the following relational expression: 0.2w2≦w1 ≦0.8w2 (1).