A compound having the following formula (I): wherein —R1 is hydrogen, optionally substituted lower alkyl, cyclo(lower)alkyl, cyclo(higher)alkyl, optionally substituted aryl, optionally substituted heterocyclyl, or aryl-fused cyclo(lower)alkyl, R2 is hydrogen or halogen, Z is CH or N, X is formula (II) R3 is lower alkyl which may be substituted with —OH or optionally substituted aryl, or lower alkanoyl, R4 is hydrogen or lower alkyl, Y is optionally substituted lower alkylene, or a salt thereof. The compound is useful as a histone deacetylase inhibitor.