A phase plate and an optical head device are provided, which are capable of suppressing changes of the amount of light incident on a light-receiving unit even if the phase difference caused by transmission through a protective layer of an optical recording medium differs depending on the type of optical recording medium.The phase plate includes a birefringent medium and produces a phase difference in linearly polarized light incident on the phase plate between a polarization component having a polarization direction parallel to the optic axis of the birefringent medium and a polarization component having a polarization direction perpendicular to the optic axis. In the phase plate, the birefringent medium includes a plurality of types of phase areas disposed adjacently; at least two types of adjacent phase areas are different from each other in phase differences, optic axes, or both phase differences and optic axes; and each of the plurality of types of phase areas is disposed so as to have two-fold rotational symmetry with respect to the optical axis of the phase plate.