The invention aims to provide a dipeptidyl peptidase IV inhibitor which is satisfactory in respect of activity, stability and safety and has an excellent action as a pharmaceutical agent. The invention is directed to a compound represented by the following general formula or a pharmaceutically acceptable salt thereof: wherein R<1> and R<2> each represents hydrogen, an optionally substituted C1-6 alkyl group, or -COOR<5> whereupon R<5> represents hydrogen or an optionally substituted C1-6 alkyl group, or R<1> and R<2>, together with a carbon atom to which they are bound, represent a 3- to 6-membered cycloalkyl group, R<3> represents hydrogen or an optionally substituted C6-10 aryl group, R<4> represents a hydrogen or a cyano group, D represents -CONR<6>-, -CO- or -NR<6>CO-, R<6> represents hydrogen or an optionally substituted C1-6 alkyl group, E represents -(CH2)m- whereupon m is an integer of 1 to 3, -CH2OCH2-, or -SCH2-, n is an integer of 0 to 3, and A represents an optionally substituted bicyclic heterocyclic group or bicyclic hydrocarbon group.
