Disclosed is a triazole derivative(s) represented by the general formula (1) below or a pharmacologically acceptable salt(s) thereof. Also disclosed are a prodrug(s) of such a triazole derivative(s) and an HSP90 inhibitor(s) 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 alkynyl 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 alkyl group or the like.)