To provide a color separation, synthetic optical device, and a projection type display device using the same by the elements easily formable with a bright optical system instead of condenser lens and dichroic mirror with thin-film wedge.

A light beam of a light source 1 is made incident on a blue/red reflective dichroic mirror 2rb, and reflected blue and red light beams are made incident on a reflective dichroic mirror 2b, and the transmitted red light is made incident to a reflection type hologram 5r with a lens function. The blue and green light beams are made incident on each surface of a reflection type hologram 5 with a lens function. A converged light beams of the red, blue, and green light pass through each of liquid crystal panels 4r, 4b, and 4g, and then, are synthesized by a reflection type hologram 6A and a reflection type hologram 6b, and are projected on a screen by a projection lens 7.