Projection image display device

After the red portion from the light source (301, 302), green, and blue colored light, at the light valve portion (304) of the valve element (317,319,321) are modulated incident on the color synthesizing optical system (305). Color synthesizing optical system (305), a three vertex angle of approximately 30 degrees prism triangular prism (325,326,327) via a dichroic mirror (328, 329) joined together. Color light incident surface of the prism with the apex angle of the pair, are synthesized in the color synthesizing optical system (305) exiting from the prism (327) of the exit surface (332). For color light, the optical path length from the incident surface to the exit surface (332) is substantially equal. Thereafter, the projection lens (306) at the enlarged and projected onto a screen. By the above-described manner, it is possible to achieve high-quality projection images and downsizing and cost reduction of the projection apparatus.