An object of the present invention is to remove or reduce iodine contained in a marine natural product extract, while maintaining the original flavor, taste, appearance, etc. of the marine natural product extract before processing. A first anion exchange membrane (5) and a second anion exchange membrane (6) are sequentially arranged from the anode (3) side. Between the anion exchange membranes (5, 6), an extract receiving compartment (9) is formed and fed with a marine natural product extract (21). An iodine recovery compartment (8) is formed on the anode side of the first anion exchange membrane (5). A replenisher receiving compartment (10) is formed on the cathode side of the second anion exchange membrane (6) and fed with a replenisher containing chlorine ions (24). During electrodialysis, the iodine ions contained in the marine natural product extract (21) pass through the first anion exchange membrane (5) and migrate into the iodine recovery compartment (8), while the chlorine ions contained in the replenisher (24) pass through the second anion exchange membrane (6) and replenish the extract receiving compartment (9).