An illumination device of the present disclosure includes: a first light source unit that emits first light of a first wavelength band; a first spatial light modulator where the first light from the first light source unit enters; a second light source unit that emits second light of a second wavelength band; an integrator optical system including a first fly-eye lens where the second light from the second light source unit enters and generating illumination light for an illumination target on a basis of the first light having been modulated by the first spatial light modulator and the second light from the second light source unit; and a multiplexing optical system that multiplexes the second light having entered the first fly-eye lens and the first light having been modulated by the first spatial light modulator, in an optical path between the first fly-eye lens and the illumination target.