Patent ID: 7126888

Claim:
An optical pickup apparatus for irradiating laser light onto an optical recording medium and for directing the light reflected from at least the optical recording medium to a light-receiving device section through a diffraction element to detect a focus-error signal by a spot size detection method using diffracted light caused by the diffraction element, wherein the position of the light-receiving device section is set to the position offset closer to the diffraction element from the focal position of the 0 order light passing through the diffraction element, and wherein the position of the light-receiving device section is offset closer to the diffraction element from the focal position of the 0 order light passing through the diffraction element as long as the following relation is satisfied: ( NA[+ 1 ]/NA[− 1])<( D 2/ D 1)≦( NA[+ 1 ]/NA[− 1]) 2 where NA[+1] indicates the numerical aperture of the +1 order light diffracted by the diffraction element; NA[−1] indicates the numerical aperture of the −1 order light diffracted by the diffraction element; D1 indicates the distance from the focal position of the +1 order light diffracted by the diffraction element to the light-receiving device section; and D2 indicates the distance from the focal position of the −1 order light diffracted by the diffraction element to the light-receiving device section.