Cross-linked rubber obtained from a rubber composition, which comprises 100 parts by weight of EPDM, 5-120 parts by weight carbon black, 70-150 parts by weight of fine bituminous powder, and 0.2-8 parts by weight of an organic peroxide, has distinguished heat resistance and sealability, and can suppress blister generation due to pressure changes when used in contact with carbon dioxide, and is specifically distinguished foaming-resistance characteristics due to abrupt pressure reduction of carbon dioxide, which are the necessary characteristics of seal material for carbon dioxide refrigerant, and also distinguished compression set characteristics, which determine the product life at elevated temperatures, and thus is suitable for use as carbon dioxide seal materials, such as O rings, packings, gaskets, oil seals, valves, etc.