The present invention is: a curable composition comprising a component (A), a component (B), and a component (C), the curable composition comprising the component (A) and the component (B) in a
mass ratio (component (A):component (B)) of 100:0.3 to 100:50, the component (A) being a curable polysilsesquioxane compound that comprises a repeating unit represented by a formula (a-1),R1SiO3 / 2 (a-1)wherein R1 is a substituted or unsubstituted
alkyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted
aryl group, the component (B) being fine particles having an average primary particle size of 5 to 40 nm, and the component (C) being a
silane coupling agent that comprises a
sulfur atom in its molecule. This invention provides: a curable composition that produces a cured product that exhibits excellent adhesion, excellent
delamination resistance, and excellent
heat resistance, and exhibits excellent workability during the application step, a method for producing the same, a cured product obtained by curing the curable composition, a method for using the curable composition as an optical element-securing
adhesive or an optical element sealing material, and an optical device.