To provide a torsional damper capable of securing vibration attenuating effect by suppressing viscous effect and spring effect of an elastomer from lowering by protecting the elastomer elastically coupling a hub and damper mass from leaking oil leaking from a bearing part of a rotary shaft.

The torsional damper has the hub 1 arranged coaxially with the rotary shaft and having an outer peripheral surface 1c, the damper mass 2 coaxially arranged in the outer peripheral side of the hub 1 spaced apart by an annular space S and having an inner peripheral surface 2a, and the elastomer 3 arranged in the annular space S and elastically coupling the hub 1 and the damper mass 2. A seal member 4 hermetically sealing the opening of the annular space S is arranged at least one side of the elastomer 3 in an axial direction of the rotary shaft.