Patent ID: 8107349

Claim:
An optical head device, comprising: a laser light source for producing a light beam; an objective lens for focusing the light beam from the laser light source on an optical recording medium and for receiving its reflected beam or a reflected light beam; an astigmatic optical element for causing the reflected light beam having passed through the objective lens to have astigmatism and thereby focus along a line in a Y direction at a near front focal line position and along a line in an X direction at a far rear focal line position, the reflected light beam having an optical axis in a Z direction, the X direction and the Y direction being orthogonal to each other in a plane perpendicular to the Z direction; and a photodetector for detecting a focus position of the objective lens from a shape of the reflected light beam, the photodetector being disposed between the front focal line position and the rear focal line position, wherein a shield plate for shielding both outer sides in a direction of width orthogonal to a longitudinal direction on a cross section of the reflected light beam at the front focal line position is disposed at the front focal line position.