The present invention relates to preventives or remedies for Alzheimer's disease, or to amyloid protein fibril-formation inhibitors, which include as an active ingredient a compound of general formula (I) below or a pharmacologically permitted salt thereof; and also to nitrogen-containing heteroaryl derivatives having specific substituents, or pharmacologically permitted salts thereof, which are valuable as preventives or remedies for Alzheimer's disease, or as amyloid protein fibril-formation inhibitors: (where, R1 and R2 are H or alkyl; Z1 and Z2 are H, alkyl, alkoxy, haloalkyl or halogeno; Z3 is alkoxy, SH, alkylthio, NH2, mono- or di-alkylamino, OH or halogeno; Z4 and Z5 are H or halogeno; and A is 4,6-pyrimidine-1,3-diyl, 1,3,5-triazine-2,6-diyl, etc).