A projector optical system for forming a real image by projecting an image of a display element is constituted by, sequentially from a projection side, an aperture diaphragm; and a first lens group having positive refractive power and having, in the interior thereof or on a lens surface at a projection side or at a display element side, a diffraction optical surface formed by a multilayer-type diffractive optical element in which diffraction gratings formed on two diffractive element components are arranged facing each other. The projector optical system is configured so as to satisfy the following expression 0.1