Objects are to obtain a highly accurate diffraction element that may prevent an intensity decrease of a light beam entering a light receiving unit without a decrease in diffraction efficiency and without a problem of flare or the like, a manufacturing method for the diffraction element, and a spectrometer using the same. A diffraction element (2) includes a diffraction grating formed on a substrate having a curved surface. In the diffraction element (2), the curved surface (3) has an anamorphic shape formed by pivoting a curved line (I) in a plane about a straight line (II) in the same plane serving as a rotation axis, and gratings (10a) of the diffraction grating (10) exist in cross sections orthogonal to the rotation axis.