PURPOSE: To obtain a small-sized projection unit which generates no color shade by performing image modulation by three light valves which are arranged at positions equal in optical path length from a light source, mixing two colors by a color mixing means, and projecting the composite color on a screen together with other one color.

CONSTITUTION: The projection light from the light source 6 is reflected by a reflector 7 and diffracted spectrally into the primary colors by dichroic mirrors 14a and 14b. Here, the mirrors 14a and 14b are arranged so that the optical path lengths from the light source 6 to the three liquid crystal light valves 9a, 9b, and 9c are equal. Then the spectrally diffracted color lights of the primary colors are image-modulated by the valves 9a, 9b, and 9c and the green light is projected on the screen by a 2nd projection lens 15b. The red light and blue light are put together by the mirror 14d and projected on the screen through a 1st projection lens 15a, so that the image is put together with the image of the green light. Consequently, the small-sized projection unit which generates no color shade and enables excellent picture element matching is obtained.