A cyclic carbodiimide compound which is useful as an end-sealing agent for polymer compounds. The cyclic carbodiimide compound is represented by the following formula (i): In the above formula, X is a divalent group or a tetravalent group represented by the following formula (i-4). When X is divalent, q is 0 and when X is tetravalent, q is 1. Ar1 to Ar4 are each independently an aromatic group. They may be substituted by an alkyl group having 1 to 6 carbon atoms or phenyl group.