A diffractive optical element capable of further reducing zero-order diffraction light includes a diffraction layer including: a high refractive index part in which a plurality of projections are arranged side by side in a cross-sectional shape; and a low refractive index part that has a lower refractive index than the high refractive index part and that includes a recess formed at least between the projections. The projections have a sawtooth shape or a shape that imitates a sawtooth shape by a multi-stage outline shape. An inclined plane that is inclined with respect to a sheet surface of the diffractive optical element, which has a sawtooth shape or a sawtooth shape imitated by a multi-stage outline shape, has a concave curved plane that is concave toward the projections.