An illuminator of the present disclosure includes a light source unit that emits at least one colored light, and emits, for each of the pieces of colored light, light having a plurality of peak wavelengths different from each other, and a diffraction device that includes a plurality of divided areas, and displays, in each of the divided areas, a diffraction pattern that is optimized at a corresponding peak wavelength out of each of the peak wavelengths. The plurality of divided areas allows the light of the plurality of peak wavelengths to enter the plurality of divided areas individually for each of the pieces of colored light.