PURPOSE: To simplify the structure of an ion exchange apparatus and to improve the efficiency for back washing and regeneration by performing ion exchange treatment by passing liquid downwards and eliminating requirement for water collecting pipe and inert resin.

CONSTITUTION: The ion exchange apparatus comprises an upper chamber and a lower chamber partitioned by a liquid permeable partitioning plate 11, and a resin transfer pipe 13 communicating the bottom of the upper chamber with the top of the lower chamber at the outside of the ion exchange column interposing a valve 14. The lower chamber contains an ion exchange resin layer 12b packed so as to form a fixed bed, and the upper chamber contains an ion exchange resin layer 12a packed so as to form a fluidized bed by the upward flow. By this construction, the structure is simplified and the efficiency for back washing and regeneration is improved.