A torsional damper is provided with: a hub affixed to a rotary shaft and having an outer-circumferential surface along a circle centered on the rotary shaft; an annular oscillation ring having an inner-circumferential surface the diameter of which is larger than the outer-circumferential surface of the hub on a circle centered on the rotary shaft; and a rubber ring that exists in a compressed state between the outer-circumferential surface of the hub and the inner-circumferential surface of the oscillation ring, comprises a rubber composition the main component of which is EPDM, and has a loss coefficient (tan δ) of 0.18 or higher when the surface temperature is 60±5° C. When subjected to resonance point tracking, the rubber thickness (c) and the maximum attained surface temperature (Tmax) of the rubber ring during continuous excitation at the resonance point satisfy a prescribed relational expression.