The present invention is to provide an aliphatic nitrogen-containing 5-membered ring compound represented by the formula [I]: wherein A represents —CH2— or —S—, R1 represents hydrogen atom, a lower alkyl group, a hydroxy lower alkyl group or a lower alkoxy lower alkyl group, X represents —N(R3)—, —O— or —CO—, where R3 represents hydrogen atom or a lower alkyl group, and R2 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.