A silicone oil (18) is filled in a housing (12) of a rotary damper (10) and a rotor brake plate (24) provided in connection with the bottom end part of a rotary shaft (22) of a rotor (20) is rotatably housed inside the housing (12). In addition, an O-ring (30) for preventing the silicone oil (18) from leaking to outside of the housing (12) is disposed between the housing (12) and the rotary shaft (22). The O-ring (30) is formed from a silicone rubber having a hardness that is between 25 and 45 according to JISK 6253 durometer hardness testing (type A).
