The present invention provides a low-molecular inhibitor of GIP functions and, further, an agent for preventing/ameliorating obesity based on inhibition of GIP functions, which comprises, as an active ingredient, a compound represented by the following general formula (I): ##STR00001## (wherein R.sup.1 represents hydrogen, halogen, a nitro group or a cyano group, R.sup.2 and R.sup.3 each represent hydrogen or halogen, hydrogen or a methoxy group, or both R.sup.2 and R.sup.3 may form an optionally substituted benzene or pyrrole ring, and A represents nitrogen or C--R.sup.4 whereupon R.sup.4 represents hydrogen, an optionally substituted C1 to C6 alkyl group, --OR.sup.7, --NR.sup.8R.sup.9, --NHCO--R.sup.10 or --SO.sub.2--R.sup.11 or may, together with R.sup.3, form an optionally substituted benzene or pyrrole ring, R.sup.7, R.sup.8 and R.sup.9 each represent hydrogen or an optionally substituted C1 to C6 alkyl group, R.sup.10 represents a C1 to C6 alkyl group or the like, and R.sup.1 represents an optionally substituted morpholyl group or the like) or a pharmaceutically acceptable salt thereof.