An objective lens for recording and/or reproducing information of an optical information recording medium, is a single lens having an aspherical surface on at least one surface. The objective lens is a finite conjugate type to converge a divergent light flux from a light source onto an information recording plane of the optical information recording medium and satisfies the following formula:

• where NA is an image-side numerical aperture necessary for conducting recording and/or reproducing information of the optical information recording medium.