A piperazine derivative represented by the formula (1): wherein n is an integer of 1 to 8; R.sup.1 represents hydrogen or C.sub.1-10 alkyl; A represents CH or nitrogen; Ar.sup.1 represents phenyl or substituted phenyl; and Y represents a group represented by the formula Y.sup.1-Y.sup.2-Ar.sup.2 or Y.sup.3-Y.sup.4(Ar.sup.5)-Ar.sup.6 or a pharmaceutically acceptable salt of the derivative. The novel piperazine derivative has MC4 receptor antagonistic activity.