A diffractive optical element according to the present invention includes: a lens body 11 with a blazed grating 13 on an aspheric surface 11a thereof; and an optical adjustment layer 15 that covers the diffraction grating 13. The lens body 11 is made of a first material 14a and the optical adjustment layer 15 is made of a second material 14b that has a higher refractive index than the first material 14a. The diffraction grating 13 has a number of ring zones that are arranged concentrically around an optical axis, where the height of each ring zone with respect to the aspheric surface 11a of the lens body 11 is represented by an increasing function of a distance r from the optical axis. The increasing function is represented by a phase polynomial that uses the distance r as a variable and that has a magnitude of 3/4π to 7/4π when r=0.