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.

Abstract: In a method of recording and/or reproducing information consisting of directory data and actual data on an optical card having first and second directory data record regions and first and second actual data record regions, the same actual data are recorded in the first and second actual data record regions, the same directory data including position data denoting tracks in the first and second actual data record regions on which the actual data have been recorded are recorded in the first and second directory data record regions. Upon reproduction, at first the directory data recorded in the first directory data record region are read out and if this directory data can be read out correctly, the actual data recorded in the first actual data record region are read out under the control of the position data included in the read-out directory data.

Abstract: An optical disk device having a head for reading information from a disk having tracks of different pitches depending upon a radial position on the disk.