To provide an electric deionizer which can avoid ion leakage to treated water due to short circuiting of water to be treated in a desalting chamber to obtain high purity deionized water, and a pure water production system equipped with the electric deionizer.

In the electric deionizer 1 made by forming concentration chambers 3 and desalting chambers 2 by alternately arranging a plurality of anion exchange membranes 5 and cation exchange membranes 4 between the cathode 6 and the anode 7, the desalting chambers 2 are filled with an open-cell structure foam having a volume larger than the capacity of the desalting chamber 2, having elasticity, and retaining a fine ion exchanger, in a compressed state.