A prism unit that combines light in the three primary colors of R, G, and B on the same optical axis includes: a G-reflecting dichroic coating that reflects G light and passes R and B light; and an RB dichroic coating that reflects one of R and B, and passes the other one of R and B, the prism unit satisfying the following conditional expression: λrg≧λrb≧0.67×λrg+0.33×λgb, where λgb represents the wavelength at which the transmittance is 50% when the colors of G and B on the composite optical axis are combined, λrg represents the wavelength at which the transmittance is 50% when the colors of R and G on the composite optical axis are combined, and λrb represents the wavelength at which the transmittance is 50% when the colors of R and B on the composite optical axis are combined.