Patent ID: 8121012

Claim:
An optical information recording/reproducing apparatus for recording information to and/or reproducing information from an optical disc based on a predetermined standard by using a light beam having a wavelength of λ (unit: nm), the optical information recording/reproducing apparatus comprising: an objective lens that converges the light beam onto a recording surface of the optical disc and satisfies a condition: 0.40 < d · ( n - 1 ) f 2 < 0.70 ( 3 ) where f represents a focal length (unit: mm) of the objective lens with respect to the wavelength λ, d represents a thickness (unit: mm) of the objective lens along an optical axis of the objective lens, and n represents a refractive index with respect to the wavelength λ; a photoreceptor that receives the light beam reflected from the recording surface of the optical disc; a detector that detects quality of a signal outputted by the photoreceptor based on the light beam reflected from the recording surface of the optical disc; and an objective lens driving unit configured to tilt the objective lens in a direction to improve the quality of the signal based on a result of detection by the detector, wherein: at least one of surfaces of the objective lens is formed to be a phase shift surface having a phase shift structure including a plurality of refractive surface zones which are concentrically formed and are divided by minute steps, each of the steps being formed at a boundary between adjacent ones of the plurality of annular zones to give a predetermined optical path length difference to the light beam incident thereon; when (Σφ 0.00-1.00 ) represents a sum of heights of all the steps formed in an effective beam diameter on the phase shift surface, and (Σφ 0.95-1.00 ) represents a sum of heights of the steps formed in a range of 95% to 100% of an effective beam radius with respect to the optical axis, the objective lens satisfies a condition: 0.2 < ( ∑ ϕ 0.95 ⁢ - ⁢ 1.00 ) ( ∑ ϕ 0.00 ⁢ - ⁢ 1.00 ) < 0.6 . ( 4 )