Prism unit and projector

A prism unit that combines light in the three primary colors of Red, Green, and Blue on the same optical axis, the prism unit comprising:

• a G-reflecting dichroic coating that reflects Green light and passes Red and Blue light;
• and an RB dichroic coating that reflects one of Red and Blue, and passes the other one of Red and Blue, wherein the prism unit satisfies the following conditional expression:
• λrg≧λrb≧0.67×λrg+0.33×λgb (1)
• where λgb represent a wavelength at which a transmittance is 50% when the colors of Green and Blue on a composite optical axis are combined in the G-reflecting dichroic coating, λrg represents a wavelength at which the transmittance is 50% when the colors of Red and Green on the composite optical axis are combined in the G-reflecting dichroic coating, and λrb represents a wavelength at which the transmittance is 50% when the colors of Red and Blue on the composite optical axis are combined in the RB dichroic coating.