A humidifier for a fuel cell includes: a housing; a first space provided in the housing; a moist air supply port connected to the housing so as to communicate with the first space and configured to supply moist air discharged from a fuel cell stack; a humidification unit provided in the first space; a second space disposed separately from the first space and provided in the housing so as to communicate with the humidification unit; and an inflow gas discharge port connected to the housing so as to communicate with the second space and configured to discharge inflow gas that has passed through the humidification unit, which can simplify a structure of the humidifier and improve spatial utilization and a degree of design freedom.