wherein n is an integer of 0 to 10; R1 represents substituted or unsubstituted lower alkyl, substituted or unsubstituted lower alkoxy, substituted or unsubstituted cycloalkyl, substituted or unsubstituted lower alkoxycarbonyl, substituted or unsubstituted heterocyclic-alkyl, substituted or unsubstituted aryl, —CONR7R8, —NR9R10, etc.; R2 represents substituted or unsubstituted aryl or a substituted or unsubstituted heterocyclic group, etc.; R3 and R5 may be the same or different, each represent a hydrogen atom, substituted or unsubstituted lower alkyl, etc.; R4 and R6 may be the same or different, each represent a hydrogen atom, halogen, substituted or unsubstituted lower alkyl, etc.) Provided are an Hsp90 family protein inhibitor comprising, as an active ingredient, a benzene derivative of formula (I) or a prodrug thereof or a pharmaceutically-acceptable salt thereof, etc.