At least one of four rectangular prisms in a dichroic prism is made longer than the other rectangular prisms. Parts of the rectangular surfaces of the long rectangular prisms partially protrude from the rectangular surfaces of the other rectangular prisms in the longitudinal direction. The protruding parts of the rectangular surfaces of the long rectangular prisms are not provided with a dichroic film. Such a construction makes it possible to prevent return light, which returns from the light emitting surface side of the dichroic prism and the dichroic prism, from emitting again from the light emitting surface.