A rotary damper has a cylindrical casing having a chamber filled with a viscous fluid, a rotor rotatably mounted in the cylindrical casing, a movable valve mounted in the cylindrical casing for adjusting a flow of the viscous fluid in the chamber, a flange mounted in the casing and having a pair of through holes defined therein and communicating with the chamber, and a torque adjustment disk angularly movably mounted in the casing and having an orifice held in communication with the through holes. The orifice has a cross-sectional area varying progressively from an end thereof toward an opposite end thereof, wherein a torque applied by the rotor can be adjusted by angularly moving the torque adjustment disk.