A first dichroic mirror (2a) and a second dichroic mirror (2b) are formed on the bonding surfaces between four right angle prisms (1a-1d) so as to intersect. The first dichroic mirror (2a) transmits, of visible light of P-polarization, at least the light of a specific wavelength band and reflects, of visible light of S-polarization, at least the light of the specific wavelength band. The second dichroic mirror (2b) transmits, of visible light of P-polarization, at least light of the specific wavelength band and transmits, of visible light of S-polarization, at least light of the specific wavelength band. The cutoff wavelengths with respect to S-polarized light of both dichroic mirrors (2a and 2b) are set within ranges of bands other than those of the three primary colors of light.