An optical pickup 1 includes a collimator lens 13 for changing the shape of a laser light by moving on the optical axis AX from a standard point. An objective lens 15 is set so as to form a spot of which size when the collimator lens 13 is located at the standard point is minimum at a point a distance apart from the surface on a light source 10 side of an information recording medium 20, the distance being a thickness to the designed center defined by an expression (1): Lc=(L0+Ln)/2   (1), wherein Lc is a thickness to the designed center; L0 is a distance between the surface on the light source side of the information recoding medium and an information recording face located nearest to the surface; and Ln is a distance between the surface on the light source side of the information recording medium and an information recording face located farthest from the surface.