A projection optical system which can project a bright image with less distortion and a small projection distance without causing aberration or an increase in size of reflective surfaces is disclosed. The projection optical system projects luminous flux from an original image onto a projection surface which is oblique to a central principal ray which is a principal ray of luminous flux traveling from the center of the original image to the center of a projected image. The projection optical system comprises a refractive optical system which includes a plurality of refractive optical elements through which the luminous flux from the original image passes through, and a reflective optical system which includes a plurality of reflective surfaces each having an optical power and guides the luminous flux emerging from the refractive optical system to the projection surface.