Provided is a damper wherein viscous fluid which fills a circular cylinder chamber is more reliably prevented from leaking.
A rotary damper (1) includes: a first seal ring (8a) of an elastic body, arranged between a through-hole (23) of a circular cylinder chamber (21) in a case (2) and a lower end of a rotor body of a rotor (3); and a second seal ring (8b) of an elastic body, arranged between a through-hole (60) in a lid (6) and an upper end of the rotor body. The first seal ring (8a) has: an outer peripheral surface with a width in a direction of a center axis of the circular cylinder chamber (21), which is pressed against an inner peripheral surface of the through-hole (23); and an inner peripheral surface with a width in the direction of the center axis of the circular cylinder chamber (21), which is pressed against an outer peripheral surface of the lower end of the rotor body, and also a second seal ring (8b) has: an outer peripheral surface with a width in the direction of the center axis of the circular cylinder chamber (21), which is pressed against an inner peripheral surface of the through-hole (60); and an inner peripheral surface with a width in the direction of the center axis of the circular cylinder chamber (21), which pressed against an outer peripheral surface of the upper end of the rotor body.