A rubber composition comprising a diene rubber and a filler; the diene rubber containing a styrene-butadiene copolymer and a natural rubber, wherein the content of the styrene-butadiene copolymer is not less than 30 mass% of the total mass of the diene rubber; a radical generation index of the styrene-butadiene copolymer being not greater than 1.0 and being smaller than a value Y calculated from Equation : Y = − 0.0186 × SV mass % + vinyl unit mol % + 1.5 where the radical generation index is an index representation of the radical concentration using the radical concentration of a copolymer having a molar ratio of styrene units/vinyl units (1,2-bonds)/trans units (trans-1,4 bonds)/cis units (cis-1,4 bonds) of 13/14/15/58 as a reference value (1.0); "SV mass%" in Equation is the mass% of a partial structure where a styrene single chain having one styrene unit and a vinyl single chain having one vinyl unit are directly linked relative to the amount of bonded styrene of the styrene-butadiene copolymer, and "vinyl unit mol%" in Equation is the mol% of vinyl units when a total of styrene units, vinyl units (1,2-bonds), trans units (trans-1,4 bonds), and cis units (cis-1,4 bonds) in the styrene-butadiene copolymer is defined as 100 mol%, and wherein the styrene single chain content having one styrene unit is not greater than 30 mass% of the amount of bonded styrene in the styrene-butadiene copolymer. the diene rubber containing a styrene-butadiene copolymer and a natural rubber, wherein the content of the styrene-butadiene copolymer is not less than 30 mass% of the total mass of the diene rubber; a radical generation index of the styrene-butadiene copolymer being not greater than 1.0 and being smaller than a value Y calculated from Equation : Y = − 0.0186 × SV mass % + vinyl unit mol % + 1.5 where the radical generation index is an index representation of the radical concentration using the radical concentration of a copolymer having a molar ratio of styrene units/vinyl units (1,2-bonds)/trans units (trans-1,4 bonds)/cis units (cis-1,4 bonds) of 13/14/15/58 as a reference value (1.0); "SV mass%" in Equation is the mass% of a partial structure where a styrene single chain having one styrene unit and a vinyl single chain having one vinyl unit are directly linked relative to the amount of bonded styrene of the styrene-butadiene copolymer, and "vinyl unit mol%" in Equation is the mol% of vinyl units when a total of styrene units, vinyl units (1,2-bonds), trans units (trans-1,4 bonds), and cis units (cis-1,4 bonds) in the styrene-butadiene copolymer is defined as 100 mol%, and wherein the styrene single chain content having one styrene unit is not greater than 30 mass% of the amount of bonded styrene in the styrene-butadiene copolymer. the radical generation index is an index representation of the radical concentration using the radical concentration of a copolymer having a molar ratio of styrene units/vinyl units (1,2-bonds)/trans units (trans-1,4 bonds)/cis units (cis-1,4 bonds) of 13/14/15/58 as a reference value (1.0); "SV mass%" in Equation is the mass% of a partial structure where a styrene single chain having one styrene unit and a vinyl single chain having one vinyl unit are directly linked relative to the amount of bonded styrene of the styrene-butadiene copolymer, and "vinyl unit mol%" in Equation is the mol% of vinyl units when a total of styrene units, vinyl units (1,2-bonds), trans units (trans-1,4 bonds), and cis units (cis-1,4 bonds) in the styrene-butadiene copolymer is defined as 100 mol%, and wherein the styrene single chain content having one styrene unit is not greater than 30 mass% of the amount of bonded styrene in the styrene-butadiene copolymer. <EOS>