The curable composition of the present invention is a thiol group and a curable composition containing the liquid poly-sulfide polymer, epoxy resin, and an amine containing at least 8% by weight, liquid polyester sulfide polymers in a molecule is HS- (RS _{x) n} -R -SH (where, R is -O-CH ₂ -O- bond is less than the average value of the divalent or trivalent organic group, n 10, including, x is an integer from 1 to 5, the average value of x is 1 to 2.5 a) it is a curable composition. The curable composition of the present invention has sufficient flexibility, and high in the degree of curing is reached with respect to the initial hardness of the final hardness. The curable composition of the present invention is an increase in hardness at the time of curing fast, low viscosity, and the flexible, water-resistant, has a chemical resistance, weather resistance is excellent properties, and civil engineering and construction adhesive because the adhesive property is favorable, and civil engineering and architectural coatings , civil engineering and construction is most suitable primers, adhesives for electric and electronic, electric and electronic potting material and adhesive for automotive, automotive primer.