Hydroxyformamidine compounds represented by the following general formula or pharmaceutically acceptable salts thereof: wherein R1 represents substituted morpholino, substituted piperidino, piperazin-1-yl, substituted piperazin-1-yl, thiomorpholin-1-yl, perhydroazepin-1-yl, perhydroazocin-1-yl, tetrahydropyridin-1-yl, pyrrolin-1-yl, etc.; X represents nitrogen or CR5; and R2 to R5 are the same or different and each represents hydrogen, C1-4 alkyl, C1-4 alkoxy, trifluoromethyl or halogeno. Drugs inhibiting 20-HETE synthase relating to contraction/dilation of microvessels, induction of cell proliferation, etc. in main organs such as kidney and cerebral vessels.