Patent ID: 7848208

Claim:
An optical head device comprising: a light source; an aberration correcting element for transmitting a beam from the light source; a light guiding portion for introducing the beam from the light source to the aberration correcting element; and an objective lens for focusing the beam having passed through the aberration correcting element on an optical information recording medium, wherein the aberration correcting element corrects a longitudinal chromatic aberration occurring in the objective lens and a longitudinal chromatic aberration occurring in the light guiding portion excluding the objective lens and the aberration correcting element based on a longitudinal chromatic aberration occurring in the aberration correcting element when the light source emits a beam having a wavelength different by a specified wavelength difference, and wherein the longitudinal chromatic aberration Δfb_obj occurring in the objective lens, the longitudinal chromatic aberration Δfb_opt-obj-ca occurring in the light guiding portion excluding the objective lens and the aberration correcting element and the longitudinal chromatic aberration Δfb_ca occurring in the aberration correcting element satisfy a condition defined by the equation: |Δ fb — obj|+|Δfb — opt - obj - ca|=|Δfb — ca| when the light source emits the beam having the wavelength different by the specified wavelength.