There is provided a curable composition having a low viscosity and high cationic curability. A curable composition including an epoxy compound of Formula (1): [in Formula (1), A is a monocyclic aliphatic hydrocarbon group optionally containing an epoxy group; R1, R2, R3 and R4 are independently a hydrogen atom or a C1-10 alkyl group; n1 and n2 are independently an integer of 2 to 6; n3 and n4 are individually an integer of 2; and n5 and n6 are individually an integer of 1], and an acid generator.