The present invention is: a curable composition comprising a component (A) and a component (B) in a mass ratio (component (A):component (B)) of 100:0.3 to 100:40, the component (A) being a silane compound copolymer that is represented by a formula (a-1), and has a weight average molecular weight of 800 to 30,000, (CHR1X0-D-SiO3/2)m(R2SiO3/2)n(CHR1X0-D-SiZO2/2)o(R2SiZO2/2)p(CHR1X0-D-SiZ2O1/2)q(R2SiZ2O1/2)r   (a-1) wherein R1 is a hydrogen atom, etc., X0 is a halogen atom, etc., D is a single bond, etc., R2 is a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, etc., Z is a hydroxyl group, etc., m and n are independently a positive integer, and o, p, q, and r are independently 0 or a positive integer, and the component (B) being a silane coupling agent that includes a nitrogen atom in its molecule. With the invention, it is possible to provide: a curable composition that produces a cured product that exhibits excellent heat resistance, excellent transparency, and high adhesion; a cured product obtained by curing the curable composition; and a method for using the curable composition as an optical device adhesive, etc.