A non-organotin-based curable composition with a level of an organotin compound of not higher than 1% by weight of all constituent compounds serving as silanol condensation catalysts, which curable composition comprises: an organic polymer having a silicon-containing group capable of crosslinking by siloxane bond formation, an amidine compound represented by the general formula: R 1 N=CR 2 -NR 3 2 (wherein R 1 is a hydrogen atom or a substituted or unsubstituted monovalent hydrocarbon group whose α-carbon to the nitrogen atom has single bonds alone, R 2 is a hydrogen atom or a substituted or unsubstituted monovalent hydrocarbon group and the two R 3 moieties each independently is a hydrogen atom or a monovalent organic group; any two or more of R 1, R 2 and the two R 3 moieties may be bound together to form a ring structure) and having a melting point of not lower than 23 oC and/or a guanidine compound represented by the general formula: R 4 N=C(NR 5 2)-NR 6 2 (wherein R 4, the two R 5 moieties and the two R 6 moieties each independently is a hydrogen atom or a non-aryl monovalent organic group selected from the group consisting of a saturated or unsaturated monovalent hydrocarbon group; a monovalent hydrocarbon group having (a) substituent (s) containing at least one heteroatom selected from among a nitrogen atom, an oxygen atom, a phosphorus atom and a sulfur atom; an amino group and an imino group; and any two or more of R 4, the two R 5 moieties and the two R 6 moieties may be bound together to form a ring structure) and having a melting point of not lower than 23 oC. which curable composition comprises: an organic polymer having a silicon-containing group capable of crosslinking by siloxane bond formation, an amidine compound represented by the general formula: R 1 N=CR 2 -NR 3 2 (wherein R 1 is a hydrogen atom or a substituted or unsubstituted monovalent hydrocarbon group whose α-carbon to the nitrogen atom has single bonds alone, R 2 is a hydrogen atom or a substituted or unsubstituted monovalent hydrocarbon group and the two R 3 moieties each independently is a hydrogen atom or a monovalent organic group; any two or more of R 1, R 2 and the two R 3 moieties may be bound together to form a ring structure) and having a melting point of not lower than 23 oC and/or a guanidine compound represented by the general formula: R 4 N=C(NR 5 2)-NR 6 2 (wherein R 4, the two R 5 moieties and the two R 6 moieties each independently is a hydrogen atom or a non-aryl monovalent organic group selected from the group consisting of a saturated or unsaturated monovalent hydrocarbon group; a monovalent hydrocarbon group having (a) substituent (s) containing at least one heteroatom selected from among a nitrogen atom, an oxygen atom, a phosphorus atom and a sulfur atom; an amino group and an imino group; an organic polymer having a silicon-containing group capable of crosslinking by siloxane bond formation, an amidine compound represented by the general formula: R 1 N=CR 2 -NR 3 2 (wherein R 1 is a hydrogen atom or a substituted or unsubstituted monovalent hydrocarbon group whose α-carbon to the nitrogen atom has single bonds alone, R 2 is a hydrogen atom or a substituted or unsubstituted monovalent hydrocarbon group and the two R 3 moieties each independently is a hydrogen atom or a monovalent organic group; any two or more of R 1, R 2 and the two R 3 moieties may be bound together to form a ring structure) and having a melting point of not lower than 23 oC and/or a guanidine compound represented by the general formula: R 4 N=C(NR 5 2)-NR 6 2 (wherein R 4, the two R 5 moieties and the two R 6 moieties each independently is a hydrogen atom or a non-aryl monovalent organic group selected from the group consisting of a saturated or unsaturated monovalent hydrocarbon group; a monovalent hydrocarbon group having (a) substituent (s) containing at least one heteroatom selected from among a nitrogen atom, an oxygen atom, a phosphorus atom and a sulfur atom; an amino group and an imino group; and any two or more of R 4, the two R 5 moieties and the two R 6 moieties may be bound together to form a ring structure) and having a melting point of not lower than 23 oC.