TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Softener: The softener is a mixture of 4-155C linear and/or branched saturated hydrocarbon, and is a liquid at room temperature.Preferred Derivative: The castor oil derivative is an acetylated derivative of castor oil. The main component of castor oil and/or its derivative is ester (glyceride) of fatty acid and glycerol. 60-98% of fatty acid comprising the glyceride is recinoleic acid. EXAMPLE - NAS-5H (softener with specific gravity of 0.823, viscosity of 11 cSt, and flash point of 146degreesC) (in weight parts) (100), Septon 4077 (hydrogenated block copolymer with number average molecular weight 260000, weight average molecular weight of 320000, and hydrogen addition rate of 90% or more) (12.5), Septon 4033 (hydrogenated block copolymer with number average molecular weight 130000, weight average molecular weight of 100000, and hydrogen addition rate of 90% or more) (12.5), Lick sizer GR-301 (acetylated recinoleic acid triglyceride with viscosity of 220 mPa.second at 25degreesC, specific gravity of 0.95, flash point of 292degreesC, iodine number of 73-79, and saponification value of 310-329 mgKOH/g, castor-oil group plasticizer) (5), 1,1-bis(5-hexyl peroxy)-3,3,5-trimethyl cyclohexane (organic peroxide with molecular weight of 358.57, decomposition temperature of 147.1degreesC and active oxygen amount of 7.52%) (0.5), CHD-4E (ethoxylated cyclohexane dimethanol diacrylate with viscosity of 50 mPa.second, specific gravity of 1.062 and molecular weight of 636, ester group cross-linking adjuvant) (5) and HP2215 (hindered phenol-phosphite-lactone group composite antioxidant) (0.2) were mixed at 180degreesC to obtain thermoplastic elastomer composition. The tensile strength, 100% modulus and elongation of the sheet obtained from the obtained elastomer composition was 2.8 MPa, 0.7 MPa, and 320%, respectively. The swelling rate of the sheet after processing at 120degreesC for 72 hours, and tensile strength of the sheet after heat-resistant aging at 120degreesC for 160 hours was 120%, and 3.3 MPa, respectively. The oil bleeding resistance, extrusion-molding property and injection moldability of the sheet were found to be favorable.