A relay optical system for a rigid endoscope has two identically formed lens systems which are arranged symmetrically to each other with respect to a plane of symmetry that is perpendicular to the optical axis. The lens systems each comprise a first biconvex lens, a biconcave lens, a rod lens having a convex lens surface facing the plane of symmetry and a concave lens surface facing away from the plane of symmetry, and a second biconvex lens, in this order as viewed from the plane of symmetry.
