The present invention provides, for example, the following compounds as a pharmaceutical composition for treating diseases induced by production, secretion or deposition of amyloid β proteins.The present invention provides a pharmaceutical composition for suppressing amyloid β production comprising a compound of the formula: wherein A is a benzene ring, a pyridine ring or a pyrimidine ring, X is sultam, lactam, sulfonamide or the like, C is substituted or unsubstituted imidazolyl, substituted or unsubstituted oxazolyl or the like, R2, R3 and R4 are each independently hydrogen, halogen, hydroxy, carboxy, substituted or unsubstituted alkyl, substituted or unsubstituted alkoxy or the like, its pharmaceutically acceptable salt or a solvate thereof.