A medicament for therapeutic and/or prophylactic treatment of neuropathic pain, which comprises a compound represented by the general formula (I) or a pharmaceutically acceptable salt thereof as an active ingredient: ##STR00001## wherein R.sup.1 represents a hydrogen atom or a hydroxyl group; R.sup.2 represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms; R.sup.3 represents a phenyl group which may have 1 to 3 atoms or substituents selected from the group consisting of a halogen atom, a hydroxyl group, an alkyl group having 1 to 3 carbon atoms, and an alkoxyl group having 1 to 3 carbon atoms, or represents --NH--R.sup.4 wherein R.sup.4 represents a phenyl group which may have 1 to 3 atoms or substituents selected from the group consisting of a halogen atom, a hydroxyl group, an alkyl group having 1 to 3 carbon atoms, and an alkoxyl group having 1 to 3 carbon atoms or hydrogen atom, and n represents 0 or 1.