Novel compound represented by the formula: ##STR1## wherein ring A, ring B and ring C each stands for an optionally substituted benzene ring; X stands for --NR-- wherein R stands for hydrogen atom or an optionally substituted hydrocarbon group, --O-- or --S--; Y stands for --(CH.sub.2)n-- wherein n denotes 1 or 2 or --NH--; and R.sup.a stands for a hydrogen atom or an optionally substituted hydrocarbon group, provided that when ring C is unsubstituted or substituted only at para-position, ring B is substituted at least at ortho-position or a salt thereof which have an excellent acyl-CoA: cholesterol acyltransferase inhibiting action and cholesterol-lowering activity, their production and medicinal use.