A rotary damper includes a driven-to-rotate member with a driven-to-rotate part for coupling to a drive member, a fixed support member for holding the driven-to-rotate member so as to rotate freely, areceiving part formed between the fixed support member and the driven-to-rotate member, a seal for sealing an outer perimeter of the receiving part so that the driven-to-rotate member and the fixed support member are capable of relative rotation, and a viscous fluid inside the receiving part for damping the relative rotation between the driven-to-rotate member and the fixed support member. The rotary damper is easy to assemble by virtue of eliminating the accumulation of unwanted air inside the receiving part. Since air does not mix with the viscous fluid, the torque precision can be made constant.