The present invention is to provide an aliphatic nitrogen-containing 5-membered ring compound represented by the formula [I]: ##STR00001## wherein A represents --CH.sub.2-- or --S--, R.sup.1 represents hydrogen atom, a lower alkyl group, a hydroxy lower alkyl group or a lower-alkoxy lower alkyl group, X represents --N(R.sup.3)--, --O-- or --CO--, where R.sup.3 represents hydrogen atom or a lower alkyl group, and R.sup.2 represents (1) a cyclic group which may be substituted, or (2) an amino group which may be substituted, or a pharmaceutically acceptable salt thereof, a method for preparing the above-mentioned compound and a pharmaceutical composition comprising the above-mentioned compound as an effective ingredient.