The present invention provides Hsp90 family protein inhibitors comprising, as an active ingredient, a benzoic acid derivative represented by General Formula (I): [wherein n represents an integer of 0 to 10; R1 represents substituted or unsubstituted lower alkoxycarbonyl, substituted or unsubstituted aroyl, or the like; R2 represents —NR14R15 (wherein R14 and R15 may be the same or different and each represents a hydrogen atom, substituted or unsubstituted lower alkyl, substituted or unsubstituted aralkyl or the like); R3 and R5 may be the same or different and each represents a hydrogen atom, substituted or unsubstituted lower alkyl or the like; and R4 and R6 may be the same or different and each represents a hydrogen atom, halogen, substituted or unsubstituted lower alkyl or the like] or a prodrug thereof, or a pharmaceutically acceptable salt of said benzoic acid derivative or said prodrug.