Compounds represented by the general formula (I), prodrugs thereof, or pharmaceutically acceptable salts of both are provided as compounds which have high DPP-IV inhibiting activity and are improved in safety, toxicity and so on: (I) ##STR00001## wherein the solid line and dotted line between A.sup.1 and A.sup.2 represents a double bond (A.sup.1.dbd.A.sup.2) or the like; A.sup.1 is C(R.sup.4) or the like; A.sup.2 is nitrogen atom or the like; R.sup.1 is hydrogen atom, optionally substituted alkly group, or the like; R.sup.2 is hydrogen atom, optionally substituted alkyl group, or the like; R.sup.3 is hydrogen atom, halogen atom, or the like; R.sup.4 is hydrogen atom, hydroxyl, halogen atom, or the like; and Y is a group represented by the general formula (A) or the like; (A) ##STR00002## [wherein m1 is 0, 1, 2 or 3; and the group (A) may be freed from R.sup.6 or substituted with one or two R.sup.6's which are each independently halogen atom or the like.]