Provided are an optical pickup apparatus and an objective lens which can appropriately record and/or reproduce information on three types of discs with different recording densities and improve the light-utilization efficiency using a simple structure. A first optical path difference providing structure is formed on an optical surface of the objective lens. The first optical path difference providing structure is a step structure in which plural ring-shaped step units each including the same number of steps are arranged concentrically about the optical axis as the center. The width w1 in the direction perpendicular to the optical axis of the highest step or the lowest step in at least one step unit in the step structure is approximately half of the average value w2 of two steps at both sides of the highest step or the lowest step in the direction perpendicular to the optical axis.