An optical pickup apparatus for detecting a symmetric S-shaped signal to
obtain a focus-error signal by an SSD method for stability in operation
is provided. In 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, 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.