To provide a curable composition comprising a polymer having a reactive silicon group as a curing component, containing no or substantially no organic metal compound, and having a high curing rate. A curable composition comprising a polymer (A) having a reactive silicon group as a curing component and comprising an amidine derivative salt (B) represented by the following formula (2) as a curing catalyst: wherein R2 is a hydrocarbon group or a hydrogen atom, each of R3 and two R4's which are independent of one another, is an organic group or a hydrogen atom, R5 is a C1-25 hydrocarbon group or a hydrogen atom, and X2 is an organic acid ion, an inorganic acid ion or a hydroxy group, and optional two or more of R2, R3 and two R4's may be bonded to form a cyclic structure.