A layered diffractive optical element is disclosed, with which a high diffraction
efficiency is attained over a broad region of used wavelengths, and with which
diffraction light of unnecessary diffraction orders can be suppressed. A diffractive
optical element of the present invention includes a plurality of diffraction gratings
made of materials with different Abbe numbers, the plurality of diffraction gratings
being layered with each other. Moreover, the partial dispersion ratio with respect
to a g-line and a F-line of the material constituting at least one of the plurality
of diffraction gratings satisfies the condition represented by a specified expression.