In an optical system, first green light reflected by a first diffractive optical element propagates in a left direction by repeating total reflection within a first light guide unit, is reflected by a third diffractive optical element, and is guided to a left eye. First red light reflected by a fifth diffractive optical element propagates in a left direction by repeating total reflection within a second light guide unit, is reflected by a seventh diffractive optical element, and is guided to a left eye. First blue light reflected by a ninth diffractive optical element is reflected by an eleventh diffractive optical element, and is guided to a left eye.