An illumination device comprises a light source (3a) that includes a solid-state light source whose peak wavelength is set in the red wavelength band, a light source (3b) that includes a solid-state light source whose peak wavelength is set in the green wavelength band, a light source (3c) that includes a solid-state light source whose peak wavelength is set in the blue wavelength band, and a color synthesis optical element (1) that combines P-polarized colored light incident from one light source (3b) and S-polarized colored light incident from the other two light sources (3a and 3c). One light source (3c) includes at least one solid-state light source whose peak wavelength is set in the wavelength band of the color corresponding to one of the other light sources (3b).