To provide a rotary damper capable of imparting stable braking force to a controlling object in a variable temperature environment.

This rotary damper 1 is provided with a part 24 having a roughly elliptical cross-section, a rotation body 20 rotatably arranged inside a casing 10, and a plate spring 30. The spring 30 is arranged in the periphery of the part 24 having a roughly elliptical cross-section of the rotation body 20 so as to be curvedly formed into a roughly elliptical cross-section shape so that the spring 30 does not rotate together with the rotation body 20 when the rotation body 20 rotates following rotating operation of the controlling object and is deformed by being pressed by curved surfaces 24a and 24b positioned in a major axis side of the outer peripheral surfaces of the part 24 having a roughly elliptical cross-section of the rotation body 20.