It is disclosed that a color separation optical system improves color reproducibility by obtaining a characteristic which approximates an ideal spectral characteristic in view of influence of polarization separation caused according to the magnitude of an incidence angle. In the color separation optical system, a curve representing a characteristic of a green-reflecting dichroic film DG has a shape along the characteristic curve representing an ideal spectral characteristic corresponding to green light. Further, the characteristic of the blue-reflecting dichroic film DB is associated with that of the green-reflecting dichroic film DG. A part, in which the transmittance of the blue-reflecting dichroic film DB changes from a low transmittance to a high transmittance, in the transmittance characteristic curve representing the characteristic of the blue-reflecting dichroic film DB is included in a predetermined wavelength region associated with the characteristic of the green-reflecting dichroic film DG.