Disclosed is a silicon-containing compound represented by the general formula (1) below. Also disclosed is a curable composition containing a silicon-containing compound represented by the general formula (1) below wherein Z is a hydrogen atom, a silicon-containing compound represented by the general formula (1) below wherein Z is a C2-4 alkenyl or alkynyl group, and a hydrosilylation catalyst. This curable composition is excellent in handling properties and curability, and enables to obtain a cured product having excellent heat resistance and flexibility. (In the formula, R-R each represents a C1-12 saturated aliphatic hydrocarbon group or a C6-12 aromatic hydrocarbon group (provided that R and R are not C1-12 saturated aliphatic hydrocarbon groups at the same time); Y represents a C2-4 alkylene group; Z represents a hydrogen atom or a C2-4 alkenyl or alkynyl group; K represents a number of 2-7; T represents a number of 1-7; P represents a number of 0-3; and M and N represent numbers satisfying the following relation: N:M = 1:1-1:100, with the total of all M's and all N's being not less than 15, which make the mass average molecular weight of the compound to be 3,000-1,000,000).