NOVELTY - An ion exchange filter (10) comprises a housing (11) with a fluid flow-in port (13) through which the fluid flows in and a fluid flow-out port (31) through which the fluid flows out; and a cartridge inside the housing in which an ion exchange resin is filled, the fluid flowing in the cartridge through the flow-in port is filtrated by the ion exchange resin and the filtrated fluid flows out through the flow-out port. The housing is provided with a casing (12) having an opened upper end and a lid (30) closing the upper end opening. A gap is formed between the housing and the cartridge.    USE - For removing impurity ion from a fluid flowing in a circuit of a fuel cell system.    ADVANTAGE - The filter is capable of being less influenced by a pressure in a circuit of a fuel cell system regardless of a material constituting the ion exchange filter. The filter has the structure effectively preventing the fluid from flowing to the joining portion between the casing the lid, and accordingly, the joining portion can maintain high joining performance without being influenced by the fluid, thus realizing high durability and ensuring high coaxing performance of the cartridge with respect to the housing. The invasion of the fluid, which is not filtrated, inside the cartridge through the engaging holes can be effectively prevented.    DETAILED DESCRIPTION - An ion exchange filter comprises a housing with a fluid flow-in port through which the fluid flows in and a fluid flow-out port through which the fluid flows out; and a cartridge inside the housing in which an ion exchange resin is filled, the fluid flowing in the cartridge through the flow-in port is filtrated by the ion exchange resin and the filtrated fluid flows out through the flow-out port. The housing is provided with a casing having an opened upper end and a lid closing the upper end opening. The lid has a peripheral edge joined and formed integrally with an upper end edge of the casing. The fluid flow-in port is provided to an outer peripheral wall of the casing at a portion above a bottom surface of the cartridge disposed inside the housing, and the fluid flow-out port is formed to the lid. A gap is formed between the housing and the cartridge so that the fluid introduced inside the gap through the fluid flow-in port flows toward the bottom portion of the housing, and the fluid then flows, in a flow passage (15) formed in the housing, upward from the bottom portion of the housing.    DESCRIPTION OF DRAWING(S) - The figure is a perspective view of an ion exchange filter which is held by a mount jig.    Ion exchange filter (10)    Housing (11)    Casing (12)    Fluid flow-in port (13)    Flow passage (15)    Fluid flow-out port (31)