Disclosed is a cyclic carbodiimide compound useful as an end-capping agent for polymer compounds. The cyclic carbodiimide compound is represented by the following formula (i):
wherein X is a specific divalent group or tetravalent group, q is 0 when X is a divalent group, while q is 1 when X is a tetravalent group, and Ar
1
to Ar
4
are selected from aromatic groups each independently optionally substituted with a group that serves as X.