To provide a water treatment device for a fuel cell used for subjecting recovery water from the fuel cell to a decarboxylation treatment and an electric deionization treatment at a low cost.

Drainage from an negative electrode chamber of an electric deionization device 4 is introduced into a central chamber 26 of an air-cleaning chamber 20 through a transfer pipe 18; and air is cleaned by injecting the air into it through a tube 21. The cleaned air is injected into a decarboxylation chamber 30, and the recovery water of the fuel cell is subjected to a decarboxylation treatment. The recovery water is sequentially run through fluorine removal chambers 70, 72 and 74 and metal removal chambers 80 and 82 via a pump 62, and supplied to the deionization chamber 4.