An optical system includes a negative refraction lens and a compensating element. The negative refraction lens is a flat plate formed by a material exhibiting negative refraction, and a surface on which light is incident and a surface from which the light is emerged are formed to be flat and parallel. The compensating element is an optical element which makes light incident at a predetermined angle, emerge at another predetermined angle. A light ray is emitted from an object point on an object plane, and reaches an image point on an image plane after being refracted twice by a negative refraction lens. The light ray is reflected by the compensating element, then refracted at an emergence-side pupil, and reaches the image point upon being reflected once again by the compensating element.