A curable composition that comprises: a linear organosiloxane compound, which is represented by an average composition formula of Formula 1 and, of which a molar ratio of an alkenyl group bound to a silicon atom with respect to the total silicon atoms ranges from 0.02 to 0.2; a crosslinking type organosiloxane compound, which is represented by an average composition formula of Formula 2, and of which a molar ratio of an alkenyl group bound to a silicon atom with respect to the total silicon atoms ranges from 0.15 to 0.35; and a hydrogen siloxane compound, which is represented by Formula 3, and of which a molar ratio of a hydrogen atom bound to a silicon atom with respect to the total silicon atoms ranges from 0.2 to 0.8, wherein the organosiloxane compound is comprised in a weight ratio of 50 parts by weight to 700 parts by weight relative to 100 parts by weight of the organosiloxane compound, wherein a molar ratio of a hydrogen atom bound to a silicon atom in the siloxane compound with respect to an alkenyl group bound to a silicon atom in the organosiloxane compounds and is in a range from 0.8 to 1.2, and wherein the hydrogen siloxane compound has a molar ratio of an aryl group of the hydrogen siloxane compound with respect to the total silicon atoms of the hydrogen siloxane compound of from 0.3 to 1.0: [Formula 1] (R 1 R 2 R 3 SiO 1/2) a (R 4 R 5 SiO 2/2) b (R 6 SiO 3/2) c (SiO 4/2) d [Formula 2] (R 7 R 8 R 9 SiO 1/2) e (R 10 R 11 SiO) f (R 12 SiO 3/2) g (SiO 4/2) h wherein R 1 to R 12 independently represent an alkoxy group, a hydroxy group, an epoxy group or a monovalent hydrocarbon group, with the provision that at least one of R 1 to R 6 is an alkenyl group and at least one of R 7 to R 12 is an alkenyl group; R's independently represent an epoxy group, an alkyl group, a halogenated alkyl group, an aryl group or an arylalkyl group; a is in a range of 0 to 0.5, b is in a range of 0.5 to 0.98, c is in a range of 0 to 0.2, d is in a range of 0 to 0.1, e is in a range of 0 to 0.5, f is in a range of 0 to 0.3, g is in a range of 0.3 to 0.85, h is in a range of 0 to 0.2, n is in a range of 1 to 10, with the provision that a+b+c+d is 1 and e+f+g+h is 1. a linear organosiloxane compound, which is represented by an average composition formula of Formula 1 and, of which a molar ratio of an alkenyl group bound to a silicon atom with respect to the total silicon atoms ranges from 0.02 to 0.2; a crosslinking type organosiloxane compound, which is represented by an average composition formula of Formula 2, and of which a molar ratio of an alkenyl group bound to a silicon atom with respect to the total silicon atoms ranges from 0.15 to 0.35; and a hydrogen siloxane compound, which is represented by Formula 3, and of which a molar ratio of a hydrogen atom bound to a silicon atom with respect to the total silicon atoms ranges from 0.2 to 0.8, wherein the organosiloxane compound is comprised in a weight ratio of 50 parts by weight to 700 parts by weight relative to 100 parts by weight of the organosiloxane compound, wherein a molar ratio of a hydrogen atom bound to a silicon atom in the siloxane compound with respect to an alkenyl group bound to a silicon atom in the organosiloxane compounds and is in a range from 0.8 to 1.2, and wherein the hydrogen siloxane compound has a molar ratio of an aryl group of the hydrogen siloxane compound with respect to the total silicon atoms of the hydrogen siloxane compound of from 0.3 to 1.0: [Formula 1] (R 1 R 2 R 3 SiO 1/2) a (R 4 R 5 SiO 2/2) b (R 6 SiO 3/2) c (SiO 4/2) d [Formula 2] (R 7 R 8 R 9 SiO 1/2) e (R 10 R 11 SiO) f (R 12 SiO 3/2) g (SiO 4/2) h wherein R 1 to R 12 independently represent an alkoxy group, a hydroxy group, an epoxy group or a monovalent hydrocarbon group, with the provision that at least one of R 1 to R 6 is an alkenyl group and at least one of R 7 to R 12 is an alkenyl group; R's independently represent an epoxy group, an alkyl group, a halogenated alkyl group, an aryl group or an arylalkyl group; a is in a range of 0 to 0.5, b is in a range of 0.5 to 0.98, c is in a range of 0 to 0.2, d is in a range of 0 to 0.1, e is in a range of 0 to 0.5, f is in a range of 0 to 0.3, g is in a range of 0.3 to 0.85, h is in a range of 0 to 0.2, n is in a range of 1 to 10, with the provision that a+b+c+d is 1 and e+f+g+h is 1.