PROBLEM TO BE SOLVED: To provide a relay optical system which is well corrected for aberrations and has a reduced effective diameter, and to provide a rigid endoscope having the same.SOLUTION: A plurality of lenses disposed in each relay optical system is symmetrically arranged about an aperture stop located at the center of the relay optical system in an optical axis direction. A lens closest to an image plane is a meniscus lens having a convex surface (first convex surface) facing the image plane, and a lens adjacent to the meniscus lens has a convex surface (second convex surface) facing the meniscus lens. A composite focal length f of the meniscus lens and the second convex surface, and a thickness L of an air layer between the meniscus lens and the second convex surface along an optical axis satisfy the following expression: 0
