To provide a diffraction optical element capable of uniformly adjusting light intensities by positions on a surface to be irradiated, an illumination optical system, an exposure apparatus, a method of manufacturing a device, and a method of designing the diffraction optical element.

The present invention relates to a method of designing a first diffraction optical element 24 and a second diffraction optical element 26 provided to the exposure apparatus including the illumination optical system which illuminates a predetermined pattern based upon light emitted by a light source apparatus and a projection optical system which projects an image of the predetermined pattern on the wafer, and diffract the light to illuminate the predetermined pattern in a superposition state, light intensity distributions in angle directions of the light diffracted by the first diffraction optical element 24 and second diffraction optical element 26 being so set that light intensity distributions in angle directions of light radiated to a plurality of positions of the wafer are equal.