An interface composed of an aqueous solution (2) supply portion capable of providing a fine hole (7) for supplying an aqueous solution (2), a water-permeable electrode (3), and a water-absorbable or water-permeable film-like membrane (5), laminated integrally, wherein the fine hole (7) for supplying the solution (2) is made in the aqueous solution supply portion at the time of use, the aqueous solution (2) is supplied through the water-permeable electrode (3) and water-absorbable or water-permeable film-like membrane (5), and, when the aqueous solution (2) reaches them, the drug or the drug-containing water-soluble layer dissolve and a locally high concentration solution of the drug is formed.