Abstract: A reflected beam 6 is diffracted by regions 7a and 7b of a hologram 71, these diffracted beams are converged or diverged, and ±1-order diffracted beams from each region are received by light-receiving regions 9a+to 9b−arranged apart from the center of the hologram by a distance almost optically equal to the distance between the center point of the hologram and a convergence (focal) point of the 0-order reflected beam. Three signals obtained from three regions of each light-receiving region are calculated to obtain a focus signal, and, at the same time, signals obtained from four regions of each light-receiving region are calculated to obtain a tracking signal, so that, by using both the ±1-order diffracted beams, a focus error signal detected by the SSD method and a tracking error signal detected by the DPD method are simultaneously obtained with high efficiency and high precision.