A curable composition that can contain a high concentration of a heterocyclic compound (A) having a triazine ring as a component which gives a cured product exhibiting a high refractive index, surface without defects such as roughness or cracks, and is unlikely to have cracks occurring on the surface thereof even when exposed to a high-temperature and high-humidity environment, a cured product of the curable composition, and a compound that may be blended to the curable composition. As a component of the composition, a triazine compound having a structure in which an optionally substituted monocyclic aromatic group(s) or an optionally substituted condensed aromatic group(s) is/are bonded to the triazine ring via an amino group, and, as a solvent, triethylene glycol dimethyl ether are used in combination.