A novel bicyclo derivative represented by the followinggeneral formula (1), or a pharmaceutically acceptable saltthereof, acts as an effective DPP-IV inhibitor:(see formula 1)One example is (2S,4S)-1-[[N-(4-methylbicyclo[2.2.2]oct--1-yl)amino]acetyl]-4-fluoropyrrolidine-2-carbonitrile).