A compound represented by the following formula (I) or a salt thereof: ##STR00001## wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 represent hydrogen atom, a halogen atom, cyano group, nitro group, a C.sub.1-4 alkyl group, a halogenated C.sub.1-4 alkyl group or a C.sub.1-4 alkoxy group, R.sup.5 represents a halogen atom, cyano group, a C.sub.1-4 alkyl group, a halogenated C.sub.1-4 alkyl group or a C.sub.1-4 alkoxy group, R.sup.6 represents a C.sub.5-7 cycloalkyl group, a substituted C.sub.5-7 cycloalkyl group, a 5 to 7-membered completely saturated heterocyclic group or a substituted 5 to 7-membered completely saturated heterocyclic group, X represents a single bond, oxygen atom, sulfur atom, NR.sup.7, --O--CH.sub.2-- or --N(R.sup.8)--CH.sub.2--, R.sup.7 represents hydrogen atom or a C.sub.1-4 alkyl group, or R.sup.7 may combine with a substituent of R.sup.6 to represent a single bond, methylene group or ethylene group, R.sup.8 represents hydrogen atom, a C.sub.1-4 alkyl group or a C.sub.7-12 aralkyl group, which is useful as an active ingredient of a medicament for prophylactic and/or therapeutic treatment of diseases caused by an activation of STAT6 and/or NF-.kappa.B.