A non-organotin curable composition comprising: an organic polymer having a reactive silicon group-containing structure; an amidine compound having a melting point lower than 23°C; and an acid anhydride and/or a carboxylic acid having a pKa of 3 to 5, wherein the reactive silicon group-containing structure of the organic polymer is represented by at least one of the following formulae to: wherein R 1 represents a divalent linkage group optionally containing a heteroatom, R 2 represents a hydrogen atom or a hydrocarbon group having 1 to 5 carbon atoms, and X represents a hydroxy group or a hydrolyzable group; wherein R 1, R 2, and X are as defined above, R 3 represents a hydrocarbon group having 1 to 5 carbon atoms and bearing an electron-withdrawing group on the carbon atom at the 1-position, R 4 represents an unsubstituted hydrocarbon group having 1 to 5 carbon atoms, a is 1 or 2, b is 0 or 1, c is 1 or 2, and the relation a + b + c = 3 is satisfied; wherein R 5 represents a hydrocarbon group having 1 to 20 carbon atoms and optionally containing a heteroatom, X is as defined above, Y represents a divalent group selected from the group consisting of -O-, -S-, -N(R 6)-, -O-C(=O)-N(R 6)-, -N(R 6)-C(=O)-O-, and -N(R 6)-C(=O)-N(R 6)-, R 6 represents a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms and optionally containing a heteroatom, and d is 1, 2, or 3; and, wherein R 7 represents a hydrocarbon group having 1 to 20 carbon atoms and optionally containing a heteroatom, X is as defined above, e is 1, 2, or 3, R 8 and R 9 each independently represent a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, an aralkyl group having 7 to 20 carbon atoms, or a silyl group, R 10 represents a divalent linkage group, and each of the two bonds from R 10 is a bond of a carbon atom, an oxygen atom, a nitrogen atom, or a sulfur atom contained in the linkage group. an organic polymer having a reactive silicon group-containing structure; an amidine compound having a melting point lower than 23°C; and an acid anhydride and/or a carboxylic acid having a pKa of 3 to 5, wherein the reactive silicon group-containing structure of the organic polymer is represented by at least one of the following formulae to: wherein R 1 represents a divalent linkage group optionally containing a heteroatom, R 2 represents a hydrogen atom or a hydrocarbon group having 1 to 5 carbon atoms, and X represents a hydroxy group or a hydrolyzable group; wherein R 1, R 2, and X are as defined above, R 3 represents a hydrocarbon group having 1 to 5 carbon atoms and bearing an electron-withdrawing group on the carbon atom at the 1-position, R 4 represents an unsubstituted hydrocarbon group having 1 to 5 carbon atoms, a is 1 or 2, b is 0 or 1, c is 1 or 2, and the relation a + b + c = 3 is satisfied; wherein R 5 represents a hydrocarbon group having 1 to 20 carbon atoms and optionally containing a heteroatom, X is as defined above, Y represents a divalent group selected from the group consisting of -O-, -S-, -N(R 6)-, -O-C(=O)-N(R 6)-, -N(R 6)-C(=O)-O-, and -N(R 6)-C(=O)-N(R 6)-, R 6 represents a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms and optionally containing a heteroatom, and d is 1, 2, or 3; and, wherein R 7 represents a hydrocarbon group having 1 to 20 carbon atoms and optionally containing a heteroatom, X is as defined above, e is 1, 2, or 3, R 8 and R 9 each independently represent a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, an aralkyl group having 7 to 20 carbon atoms, or a silyl group, R 10 represents a divalent linkage group, and each of the two bonds from R 10 is a bond of a carbon atom, an oxygen atom, a nitrogen atom, or a sulfur atom contained in the linkage group.