To make total transmitted light quantity maximum and to obtain a bright and excellent observed image by including at least two or more surfaces having optical refractive power between an object image and a pupil position and satisfying a specified condition.

An optical system consisting of two or more rod lenses and reforming the object image at a desired position is an afocal system, and includes two or more surfaces having the optical refractive power between the object image and the pupil position and satisfies the conditions 0.35≥D1/1≥0.095 and l=D1+D2+D3, provided that D1 is a distance between the object image and the surface nearest to the object side out of the surfaces having the optical refractive power, D2 is a distance between the surface nearest to the object side and the surface nearest to the pupil position side out of the surfaces having the optical refractive power, and D3 is a distance between the surface nearest to the pupil position side out of the surfaces having the optical refractive power and the pupil position. The example is expressed as constitution shown in the figure. In such a case, the ratio of the transmitted light quantity is increased, so that peripheral aperture efficiency is set to about 70% with respect to center.