Anti-dementia medicaments comprising a carbamic acid derivative or their pharmaceutically acceptable acid addition salts having an anti-amnesic activity as an active ingredient are provided. The carbamic acid derivatives are represented by a general formula (1) ##STR1## wherein Ar denotes an aromatic heterocyclic ring which may have at least one substituent or its benzene-condensed ring, or phenyl group which may have at least one substituent, R.sup.1 denotes hydrogen atom or lower alkyl group, R.sup.2 denotes lower alkyl group which may be substituted with halogen atom, phenyl group which may have at least one substituent, naphthyl group, or five- or six-membered heterocyclic ring and its benzene-condensed ring, X and Y, which may be the same or different, denote sulfur atom or oxygen atom.