Abstract: A damping device for damping the relative rotation of a rotating member. The damping device includes a casing, a rotor disposed in an interior space of the casing, and a damping mechanism including a viscous liquid disposed in an annular chamber formed between the casing and the rotor. The viscous liquid exerts frictional forces to damp the relative rotation between the rotor and the casing in a first rotation direction but not in the opposite rotation direction, the damping force increasing when the rotor and the casing rotate relative to each other from a first relative angular position to a second relative angular position in the first rotation direction. The casing and the rotor are structure to provide a damping force by impeding the flow of the viscous liquid within the chamber, and to provide another damping force by the contacting of the rotor and the casing. A valve is further provided within the chamber to restrict the flow of the viscous liquid.