Disclosed is a triazole derivative represented by the general formula (1) below or a pharmacologically acceptable salt thereof. Also disclosed are a prodrug of such a triazole derivative and an HSP90 inhibitor containing any one of them as an active constituent. (1) (In the formula, X represents a halogen atom, an optionally substituted alkyl group, an optionally substituted alkenyl group or the like Y represents a mercapto group, a hydroxyl group, an optionally substituted sulfonyl group, an optionally substituted amino group or the like and R represents an optionally substituted aryl or amino group or the like.)
