A projection optical system in which an image of a first surface is projected onto a second surface based on a light beam having a predetermined wavelength. The projection optical system having at least one isometric system refractive member made of an isometric system crystal material. The isometric system crystal material transmits a light beam having the predetermined wavelength. The projection optical system also has an amorphous refractive member made of an amorphous material for compensating deterioration of optical performance due to intrinsic birefringence of the isometric system refractive member.