Provided are an iron-supplying agent which can supply a water-soluble iron ion stably for a long period of time even under an alkaline condition where an iron ion tends to become insoluble using a naturally derived raw material, and an iron-supplying agent which can supply a water-soluble iron ion using only a raw material which is safe for ingestion in the human body. Also provided is an iron-supplying agent which can supply a water-soluble iron ion (in particular, a divalent iron ion) using trivalent iron as an iron-supplying source. Also provided are a water-soluble iron-supplying agent including a reaction product as an active ingredient, in which the reaction product is obtained by using roasted and ground coffee beans and/or tea leaves as feedsotcks for supplying a metal ion-solubilizing component, and mixing the feedstocks for supplying the metal ion-solubilizing component with an iron-supplying source containing trivalent iron in the presence of water specifically, a water-soluble iron-supplying agent which can reduce trivalent iron into a divalent iron ion and maintain the divalent iron ion to supply a water-soluble iron ion (divalent iron ion) stably for a long period of time.
