A rubber composition contains: (A) an ethylene-α-olefin-based copolymer rubber including an ethylene unit and an α-olefin unit having 3 or more carbon atoms; (B) a fire retardant including a phosphorus atom and a nitrogen atom; (C) a thermally expandable graphite; and (D) additive particles that are porous particles or particles having ion exchangeability. A content of the fire retardant is 50 to 250 parts by mass and a content of the additive particles is 15 parts by mass or less with respect to 100 parts by mass of the ethylene-α-olefin-based copolymer rubber.