To provide a three-plate type projector color-combining system which can realize miniaturization and reduction in cost without reducing the optical performance.

A liquid crystal panel (R) 4, a liquid crystal panel (G) 5, and a liquid crystal panel (B) 6 for passing each light are disposed so that each optical axis have a difference of 90 degrees. A mirror 3 rotating at the position, where the optical axis form each liquid crystal panel crosses, is disposed. The mirror 3 has reflective surfaces on the both sides. When the mirror 3 is turned clockwise by the 45 degrees with respect to the optical axis B, the reflectivity of the light from the liquid crystal panel (R) 4 becomes maximum, and the reflected light is made incident on a projection lens 2. When the mirror 3 is turned by 90 degrees with respect to the optical axis B similarly, the light being made incident on the projection lens from the liquid crystal panel (G) 5 becomes maximum. When is turned by the furthermore 45 degrees, the reflectivity of the light from the liquid crystal panel (B) 6 becomes the maximum, and the reflected light is made incident on the projection lens 2. An image by the light combined with the projection lens is magnified and projected on a screen 1.