A diffraction optical device includes a first diffraction element and a second diffraction element arranged adjacent to each other. One of the first diffraction element and the second diffraction element has a positive power, and the other has a negative power. The first diffraction element reduces the incident angle of light upon the second diffraction element. As a result, a lowering of diffraction efficiency due to the dependency thereof upon the incident angle of light is suppressed, and flare light is prevented from occurring due to diffracted light of unnecessary orders.