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.
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