Patent ID: 8040779

Claim:
An optical pickup device comprising: a laser light source; an objective lens which converges laser light emitted from the laser light source on a recording medium; an astigmatism element which imparts astigmatism to the laser light reflected on the recording medium to set a first focal line position to be defined by convergence of the laser light in a first direction, and a second focal line position to be defined by convergence of the laser light in a second direction perpendicular to the first direction away from each other in a propagating direction of the laser light; a diffraction element which diffracts four light fluxes obtained by dividing a light flux of the laser light reflected on the recording medium by a first straight line and a second straight line respectively in parallel to the first direction and the second direction to disperse the four diffracted light fluxes from each other; and a photodetector including a first sensing section and a second sensing section which respectively receive m-th order diffraction light and n-th order diffraction light (where m≠n) of the four light fluxes, wherein the first sensing section is configured to receive eight light fluxes obtained by dividing the four light fluxes of the m-th order diffraction light by two straight lines respectively intersecting with the first straight line and the second straight line by 45° to output detection signals of the number less than eight.