TECHNOLOGY FOCUS - POLYMERS - Preferred Composition: The sealing material further contains 0.1-5 parts weight of silane coupling agent, 0.1-2.5 parts weight of cross-linking agent, 0.05-5 parts weight of cross-linking adjuvant and 0.005-5 parts weight of ultraviolet absorber, heat-resistant stabilizer and/or hindered amine type optical stabilizer with respect to 100 parts weight of polyene copolymer. The resin composition contains copolymer (50-95 mol%), paraffinic oil having paraffinic component (55-90 weight%), aroma component (less than 5 weight%), naphthene component (less than 40 weight%) and sulfur component (200 ppm or less), and cross-linking agent. Preferred Properties: The sealing material has volume resistivity of 1x 1013 to 1x 1018 Omega .cm. The cross-linking agent is organic peroxide having half life temperature of 100-170 degrees C for 1 minute. The polyene copolymer satisfies relation given by: B=(c+d)/(2x ax (e+f))=0.9-1.3 (a is ratio of structural unit originating in ethylene, c is ratio of structural unit originating in ethylene-( alpha )-olefin, d is ratio of structural unit originating in ethylene and non-conjugated polyene, e is ratio of structural unit originating in ( alpha )-olefin and f is ratio of structural unit originating in non-conjugated polyene). The ratio of maximum value and minimum value of ethylene distributed parameter is 1.4 or less. The copolymer has activated energy of 28-35 kJ/mol and molecular weight distribution of 1.2-3.5. The content of chloride ion detected from extract after solid phase extraction measured by ion chromatography is 2 ppm or less. The extraction amount of methyl acetate is 5 weight% or less. The copolymer has melting point of 70 degrees C or less according to JIS-K7121. The hardened material of sealing material has light transmittance of 90% or more. Preferred Additive: The additive is chosen from cross-linking adjuvant ultraviolet absorber, weathering stabilizer, antioxidant and adhesive imparting agent. Preferred Method: The sealing material is obtained by extrusion molding of copolymer and additive. The die temperature of extruder during molding is 55-120 degrees C.