The invention provides 2''-hydroxynicotianamine; a method for producing 2''-hydroxynicotianamine comprising the step of obtaining an extract solution from a buckwheat sample followed by obtaining a fraction having an inhibitory activity for the angiotensin-converting enzyme by ion-exchange chromatography using an anion exchange resin; novel substances having an ACE inhibitory activity by preparing an inhibitor for the angiotensin-converting enzyme, a vasodepressor agent and a health food each containing 2''-hydroxynicotianamine; methods for producing the novel substances; an inhibitor for the angiotensin-converting enzyme and a vasodepressor agent having the novel substance as an effective ingredient; and a health food containing the novel substance.