The present invention is: a curable composition having components (A) through (E), the curable composition characterized by containing component (A) and component (B) in a mass ratio of [component (A):component (B)] = 100:0.3-100:20; a cured material; a method of using the curable composition; and an optical device. Component (A): a silane compound copolymer represented by formula (a-1) (where X0 represents a cyano group or the like, D represents a single bond or the like, R1 represents a hydrogen atom or the like, R2 represents a C1-20 alkyl group or the like, Z1-Z4 represent hydroxyl groups or the like, m and n represent positive integers, and o-r represent 0 or positive integers). Component (B): microparticles having an average primary particle diameter of more than 0.04 µm to less than or equal to 8 µm. Component (C): a silane coupling agent having a nitrogen atom. Component (D): a silane coupling agent having an acid anhydride structure. Component (E): a silane coupling agent having a sulfur atom-conta
