Abstract: A viscous and rubber-type torsional damper including a boss portion, a pulley portion, and connecting members for elastically connecting the boss portion and the pulley portion. The connecting portions are spaced from each other in an axial direction of the torsional damper and define a fluid-tight closed space therebetween. At least one protrusion is formed on at least one of the boss portion and the pulley portion. The protrusion protrudes into the closed space and a gap is formed between the surfaces of the protrusion and the surfaces opposing the protrusion. The area between the surfaces is filled with a viscous fluid such as a silicone oil. Due to this structure, the viscous damping ability of the damper is increased without increasing the radial size of the damper and without increasing the number of constructing members of the damper.