An optical head device 201 includes a light source 1, an objective lens
group 13, a two-dimensional actuator 15, spherical aberration adding
means 9, 10, and 16, a hologram element 17 for splitting the light beam
from the optical disk 14 into a plurality of split light beams, and a
photodetector 22 which includes at least one photoreceptor including a
plurality of split light receiving areas and outputs an electric signal
corresponding to the light amount of a split light beam entering each of
the plurality of split light receiving areas or an electric signal
corresponding to a combination of the light amount of split light beams
entering the corresponding split light receiving areas, and the plurality
of split light beams split by the hologram element 17 include one
circular ray U1 and at least two annular rays U2 and U3.