Abstract: An optical disk apparatus of this invention includes a light source, an objective lens which focuses a laser beam output from the light source onto an optical disk, a hologram which divides an overlap region where, of reflected light components from the optical disk, a 0th-order light component and ±1st-order light components that are symmetrical with respect to the 0th-order light component overlap by the diameter of the 0th-order light component and also divides a non-overlap region where the 0th-order light component and ±1st-order light components do not overlap along the diameter and a radius perpendicular to the diameter, and a photodetector which independently detects reflected light components from the regions divided by the hologram.