A rubber-metal composite body constituted of a rubber composition and a metal material embedded therein is conventionally used in a rubber article requiring high strength in order to reinforce rubber to improve strength and durability thereof. The present invention provides a rubber composition having good initial adhesive properties and good heat resistant adhesive properties with respect to a metal material, mainly for use in the rubber-metal composite body as described above. Specifically, the present invention provides a rubber composition, containing a cobalt compound by an amount, according to cobalt atoms, in the range of 0.0025 to 0.05 parts by mass with respect to 100 parts by mass of a rubber component.