A projection optical system and a projection display device using the same is provided, wherein the projection optical system has a sufficiently small size to be provided in a front-projection-type projector and can effectively correct various aberrations. An original image on an image display surface is enlarged and projected onto a screen by a first optical system that includes a plurality of lenses and a second optical system that includes a reflecting mirror having a concave surface with an aspheric shape. All of the optical surfaces of the first optical system and the second optical system are rotationally symmetric surfaces each having the optical axis common to all of the optical surfaces as its center. A first lens surface, which is a reduction-side surface, and a second lens surface, which is a magnification-side surface, of a lens (fourteenth lens) closest to a magnification side in the first optical system satisfy predetermined conditional expressions.