A working electrode assembly for iontophoresis having a working electrode, a medicine-containing portion containing an ionic medicine, and an ion-exchange membrane arranged between the working electrode and the medicine-containing portion, wherein said ion-exchange membrane has both the anion-exchange groups and the cation-exchange groups, and between these anion-exchange groups and cation-exchange groups, the ion-exchange groups of the one side are contained in an excess amount compared to the other ion-exchange groups. The working electrode assembly effectively prevents the contact between the medicine and the working electrode and, at the same time, accomplishes a high efficiency for administering the medicine.