OPTICAL PICKUP APPARATUS, AND OPTIMAL LIGHT SPOT FOCUSING METHOD

PROBLEM TO BE SOLVED: To provide an optical pickup device and an optimal light spot focusing method. SOLUTION: The optical pickup device includes a diffraction member which has a first diffraction region having a wide width in a direction corresponding to the tangential direction of a recording medium, and second to fifth diffraction regions sequentially arranged around the outside of the first diffraction region in a direction corresponding to the radial direction of the recording medium, divides a first light beam made incident and reflected by the recording medium into five optical regions, and diffract the light beam into 0 order and ±1 order light beams, and a first photodetector having first to fifth light receiving portions which receives and photoelectrically transduces the first light beam reflected by the recording medium and diffracted by the first to fifth diffraction regions of the diffraction member. The first light receiving portion has four-divided light receiving regions divided into the radial and tangential directions to receive the +1 order or the -1 order beams diffracted by the first diffraction region. The second to fifth light receiving portions has single and/or two-divided light regions to receive the +1 order or the -1 order beams diffracted by the second to fifth diffraction regions.