The present invention relates to a humidifier for a fuel cell, comprising: a humidifying module for humidifying dry gas supplied from the outside, by using wet gas discharged from a fuel cell stack; a first cap coupled to one end of the humidifying module; and a second cap coupled to the other end of the humidifying module, in which the humidifier comprises a first packing member which is airtightly coupled to one end of the humidifying module through mechanical assembly, so that the first cap can be in fluid communication only with hollow fiber membranes, wherein the humidifying module comprises a first sub-case having a first insertion groove into which the first packing member is inserted.