The present invention provides a diffraction element and an optical disk drive capable of improving the flexibility for setting the aperture and the optical magnification by making it possible to set the spot shape of the main beam and the diffraction efficiency as desired. In the optical disk drive 1, the diffraction element 8 for forming three beams has a high +-primary diffraction efficiency at the center area 86 in the length direction of the groove 81 and a low +-primary diffraction efficiency at both ends 87, 88. Accordingly, since the 0th light from the center area 86 loses its light intensity largely but the 0th light from both ends 87, 88 loses its light intensity less, the shape of the peak of the 0th light has raised skirts and an equivalent effect is obtained as increasing the NA. Thus, the main beam spot can be made small in diameter when focusing it on the optical recording disk 10. Further, since wasteful high order diffraction light is not generated, the sub-spot can be made large. |