The present invention relates to a fuel cell humidifier comprising: a humidifying module for humidifying dry gas, supplied from outside, by using wet gas discharged from a fuel cell stack; and a first cap coupled to one end of the humidifying module, wherein the humidifying module comprises a mid-case, and at least one cartridge which is disposed in the mid-case and accommodates a plurality of hollow fiber membranes. The fuel cell humidifier further comprises a first packing member airtightly coupled to at least one end of the humidifying module through mechanical assembly so that the first cap may fluidly communicate with only the hollow fiber membranes, wherein the first packing member tightly adheres to the cartridge by using the pressure of at least one among the dry gas and wet gas.