A silicon-containing curing composition comprising: 100 parts by mass of a silicon-containing polymer having a weight average molecular weight (polystyrene equivalent molecular weight) of 300 to 100,000 obtained by hydrolysis and condensation of an organosilane mixture consisting of (a) 5 to 50 mol% of one or more than one organosilane represented by general formula, (b) 0 to 50 mol% of one or more than one organosilane represented by general formula, (c) 0 to 40 mol% of one or more than one organosilane represented by general formula, (d) 0 to 50 mol% of one or more than one organosilane represented by general formula, and (e) 0 to 40 mol% of one or more than one organosilane represented by general formula, the sum of the organosilane (b) and the organosilane (c) being 5 to 60 mol%; 0 to 200 parts by mass of a prepolymer containing at least two Si-H groups per molecule obtained by hydrosilylation between (a) at least one compound selected from a cyclic siloxane compound represented by general formula and (β) at least one compound selected from a compound represented by general formula, a compound represented by formula, and a compound represented by general formula; 0.1 to 30 parts by mass of a linear siloxane compound containing at least two carbon-carbon double bonds reactive with an Si-H group or an Si-CH 3 group per molecule; 0.0001 to 10 parts by mass of an organic peroxide and 0 to 1.0 part by mass of a metal catalyst; and 0 to 1500 parts by mass of a filler. R 1 SiX 3 R 2 SiX 3 R 3 R 4 SiX 2 R 5 Si X 3 R 6 S i X 3 wherein R 1 represents an alkenyl group having 2 to 6 carbon atoms; R 2 represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms; R 3 and R 4 each independently represent a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or a phenyl group optionally substituted with an alkyl group having 1 to 6 carbon atoms; at least one of R 2, R 3, and R 4 is a methyl group; R 5 represents a phenyl group optionally substituted with an alkyl group having 1 to 6 carbon atoms; R 6 represents an epoxy group having 2 to 10 carbon atoms; and X represents a hydroxyl group, an alkoxy group having 1 to 6 carbon atoms, or a halogen atom. wherein R 7, R 8, and R 9 each independently represent an alkyl group having 1 to 6 carbon atoms or a phenyl group optionally substituted with an alkyl group having 1 to 6 carbon atoms; fR 7 's may be the same or different; gR 8 's may be the same or different; gR 9 's may be the same or different; f represents a number of 2 to 10; g represents a number of 0 to 8; and f+g≥2. wherein R 10 represents an alkenyl group having 2 to 10 carbon atoms; R 11 and R 12 each independently represent an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or an epoxy group having 2 to 10 carbon atoms; and n represents 1 or 2. 100 parts by mass of a silicon-containing polymer having a weight average molecular weight (polystyrene equivalent molecular weight) of 300 to 100,000 obtained by hydrolysis and condensation of an organosilane mixture consisting of (a) 5 to 50 mol% of one or more than one organosilane represented by general formula, (b) 0 to 50 mol% of one or more than one organosilane represented by general formula, (c) 0 to 40 mol% of one or more than one organosilane represented by general formula, (d) 0 to 50 mol% of one or more than one organosilane represented by general formula, and (e) 0 to 40 mol% of one or more than one organosilane represented by general formula, the sum of the organosilane (b) and the organosilane (c) being 5 to 60 mol%; 0 to 200 parts by mass of a prepolymer containing at least two Si-H groups per molecule obtained by hydrosilylation between (a) at least one compound selected from a cyclic siloxane compound represented by general formula and (β) at least one compound selected from a compound represented by general formula, a compound represented by formula, and a compound represented by general formula; 0.1 to 30 parts by mass of a linear siloxane compound containing at least two carbon-carbon double bonds reactive with an Si-H group or an Si-CH 3 group per molecule; 0.0001 to 10 parts by mass of an organic peroxide and 0 to 1.0 part by mass of a metal catalyst; and 0 to 1500 parts by mass of a filler.