An optical element of which diffraction efficiency hardly varies with wavelength is provided by using an optical material satisfying the conditions that n_d-6.66710^-3_d+1.70 and _g,F-210^-3_d+0.59 where n_d is a refractive index at d-line, _d is an Abbe number at the d-line, and _g,F is a second order dispersion at d-line, whereby diffraction efficiency is improved in any working visible wavelength region and more precise chromatic aberration correction is obtained.