An elastomeric copolymer of an aromatic vinyl compound and butadiene prepared by a solution polymerization method, which has a glass transition temperature of not less than -50°C and contains polymer chains modified with a trifunctional or tetrafunctional coupling agent, and which contains not less than 3 % by weight to less than 23 % by weight, based on the whole polymer chains, of polymer chains having a molecular weight of at least 5 times a molecular weight corresponding to a peak appearing on the low molecular weight side of a high performance liquid chromatogram of the elastomeric copolymer. The elastomer- ic copolymer has an excellent processability and shows a low rolling resistance and a high wet grip characteristic when used as a rubber component in tires.