Reverse hydroxamic acid derivatives having specific structure represented by a general formula (Ia): ##STR00001## (wherein A is a hydrogen atom or the like; Ar.sup.1 is an arylene or the like; Ar.sup.2 is an optionally substituted aryl, a heteroaryl or the like; R.sup.1 is a hydrogen atom, an alkyl or the like; R.sup.2a is a substituted cycloaryl, a heterocycloaryl or the like) and a general formula (I): ##STR00002## (wherein A, Ar.sup.1, Ar.sup.2, and R.sup.1 are the same as defined above and R.sup.2 is an hydrogen atom, R.sup.2a or the like) and salts thereof, which have TNF-.alpha. converting enzyme (TACE) inhibitory activity.