The present invention provides an objective lens, an optical head apparatus, an optical information apparatus, and an information processing apparatus that improve focal position detection accuracy. In order to reproduce information from an optical disk (28), an objective lens (25) collects a diffracted ray (15X) having a longer focal length, out of two diffracted rays (15X, 15Y), on an information recording surface (28L) via a base (28S) of the optical disk (28), and a distance (DF3) between the focal positions of the two diffracted rays (15X, 15Y) when the diffracted ray (15X) having a longer focal length is collected on the information recording surface (28S) is longer than double the distance (WD2) between the surface (25A) of the objective lens (25) and the surface (28A) of the base (28S) along the optical axis.