The present invention provides a vulcanizable rubber composition containing (A) an ethylene/α-olefin/nonconjugated polyene copolymer rubber, (B) a polyolefin resin and (C) a blowing agent, wherein the polyolefin resin (B) is microdispersed in a melted state in the ethylene/α-olefin/nonconjugated polyene copolymer rubber (A), the polyolefin resin (B) having an average dispersed particle diameter of 2 μm or less, the polyolefin resin (B) is present in an amount of from 5 to 15 parts by mass per 100 parts by mass of the ethylene/α-olefin/nonconjugated polyene copolymer rubber (A), the blowing agent (C) is present in an amount of from 2 to 6 parts by mass per 10 parts by mass of the ethylene/α-olefin/nonconjugated polyene copolymer rubber (A), and the vulcanizable rubber composition has a specific gravity of from 1.05 to 1.15 and a Mooney viscosity (Vm) at 125° C. of from 25 to 55.