PURPOSE: To simultaneously perform the separation due to the difference in polarity and the separation of a large molecule due to the size of pores, in an ion separator used in electrodialysis, by arranging a porous dielectric or porous semiconductor electrode between two kinds of solvents to form dielectric charge.

CONSTITUTION: In an in separator, a porous dielectric or porous semiconductor electrode 1 is arranged so as to separate a solvent A and a solvent B. When positive voltage is applied between the electrode 1 and an opposed electrode 2 to charge the electrode 1 positively, H+(hydrogen ion) electrically receives repulsion and cannot pass through the electrode 1. However, when negative voltage is applied to the electrodes 1, 2, H+ is electrically attracted to pass through the electrode 1. Therefore, H+ moves from the solvent A to the solvent B and H+ concn. (PH) changes. Especially, when the porous semiconductor electrode is used as the electrode 1, by irradiating the electrode with light on the ion outlet side thereof, only the ion passed through the electrode 1 can be oxidized and reduced. Further, the size of a passing ion can be controlled according to the size of pores 10.