A projection optical system substantially consists of a first optical system composed of a plurality of lenses and a second optical system composed of one reflection mirror having a convex aspherical surface arranged in this order from the reduction side and is configured, when an air space between the first optical system and the second optical system is taken as T12 and a displacement in a direction of the optical axial from a position of maximum effective height on the magnification side lens surface of the lens disposed on the most magnification side in the first optical system to the vertex of the lens surface is taken as Zf, to satisfy a conditional expression (1): 0.1