A projection display device is provided having a mounting mechanism of a modulation element which does not cause pixel displacement at variable temperature when the pixel pitch is reduced. The projection display device is provided with a frame fixed to the light incident face of a prism composite, an intermediate frame detachably mounted to the fixed frame, a screw for fixing the fixed frame and the intermediate frame, a modulation element frame detachably mounted to the intermediate frame for holding a modulation element, a wedge for positioning the modulation element frame and the intermediate frame, and an adhesive layer for fixing the modulation element frame to the intermediate frame with the wedge therebetween. The intermediate frame is provided with a slit which facilitates elastic deformation of portions other than the fixed section for fixing the wedge.