A high specific-gravity EPDM composition consisting of a mixture of EPDM containing diene at less than 4.5 wt % and ethylene at not less than 58 wt % nor more than 80 wt % and having a Mooney viscosity ML₁₊₄ not less than 50 nor more than 170 at 125 C. and a powdery material, containing powder whose specific gravity is not less than 12 as a main component thereof, added to the EPDM at not less than 80 wt % nor more than 97.5 wt % of a whole amount of the high specific-gravity EPDM composition.