The present invention provides an electrode device used in iontophoresis treatment, in which an electrode layer used for introduction of medication can be contacted to a medication reservoir layer with a simple manner, and in which the medication reservoir layer can be reliably held when the medication is introduced into a skin. A main-electrode layer 3 and a sub-electrode layer 1 are secured on a substrate 6 while both the layers are being insulated from each other. The main-electrode layer 3 is intended for introduction of the medication, and the sub-electrode layer 1 is provided to hold the medication reservoir layer 5 on the substrate 6. The medication reservoir layer 5 is located on the substrate 6, so as to be in contact with the main-electrode layer 3 and the sub-electrode layer 1. The medication reservoir layer 5 is a gel containing halogen compound, and the sub-electrode layer 1 comprises a metal having a lower ionization tendency than hydrogen. The medication reservoir layer 5 and the sub-electrode layer 1 are bonded to each other by applying an electric current to both layers. In this way, the medication reservoir layer 5 can be firmly held on the substrate 6, while being kept in contact with the main-electrode layer 3.