A rubber composition containing carbon black for blending with rubber which is obtained in a reaction equipment continuously provided with a combustion gas-generating zone, a reaction zone and a reaction-stopping zone by producing a high temperature combustion gas in the combustion gas-generating zone, subsequently spraying and introducing a raw material into the reaction zone to form a reaction gas stream containing carbon black and then quenching the above reaction gas stream by a multistage quenching medium-introducing means in the reaction-stopping zone to terminate the reaction, wherein the above carbon black for blending with rubber satisfies the following relational equations and: 10 < X < 40 90 < Z < 100 (wherein X represents a toluene extract light transmittance (%) (measured by a method described in an eighth item B method of JIS K6218: 1997) of the carbon black after introducing a first quenching medium from a raw material-introducing position, and Z represents a toluene extract light transmittance (%) (measured by a method described in an eighth item B method of JIS K6218: 1997) of the carbon black after introducing a final quenching medium) and the above carbon black for blending with rubber is contained in a proportion of 10 to 250 parts by mass based on 100 parts by mass of a rubber component containing a conjugated diene based rubber, characterised in that a hydrogen discharge rate of the carbon black for blending with rubber is higher than 0.30 % by mass as determined by a carbon black sample is dried in an isothermal drier of 105°C for one hour and then cooled down to room temperature in a desiccator, about 10 mg of the sample is precisely weighed into a tubular sample vessel made of tin, pressed and tightly stoppered and an amount of a hydrogen gas generated when heating the sample at 2000°C for 15 minutes under argon flow is measured by means of a hydrogen analytical equipment (EMGA621W, manufactured by HORIBA, Ltd.) and shown by mass percentage. the above carbon black for blending with rubber satisfies the following relational equations and: 10 < X < 40 90 < Z < 100 (wherein X represents a toluene extract light transmittance (%) (measured by a method described in an eighth item B method of JIS K6218: 1997) of the carbon black after introducing a first quenching medium from a raw material-introducing position, and Z represents a toluene extract light transmittance (%) (measured by a method described in an eighth item B method of JIS K6218: 1997) of the carbon black after introducing a final quenching medium) and the above carbon black for blending with rubber is contained in a proportion of 10 to 250 parts by mass based on 100 parts by mass of a rubber component containing a conjugated diene based rubber, characterised in that a hydrogen discharge rate of the carbon black for blending with rubber is higher than 0.30 % by mass as determined by a carbon black sample is dried in an isothermal drier of 105°C for one hour and then cooled down to room temperature in a desiccator, about 10 mg of the sample is precisely weighed into a tubular sample vessel made of tin, pressed and tightly stoppered and an amount of a hydrogen gas generated when heating the sample at 2000°C for 15 minutes under argon flow is measured by means of a hydrogen analytical equipment (EMGA621W, manufactured by HORIBA, Ltd.) and shown by mass percentage.