An apparatus/system for generating a high-purity nitrogen gas using a fuel cell includes; a fuel cell that operates by taking in air or a gas containing nitrogen and oxygen, and a fuel gas; a dehumidification mechanism that reduces moisture or water vapor content in an exhaust gas that is extracted from the fuel cell and has a lower oxygen concentration than air; and a filtering mechanism which includes a filter using fibers having different degrees of permeation for nitrogen and oxygen and converts the exhaust gas having a reduced moisture or water vapor content into a gas having an increased nitrogen concentration. The filter recovery ratio is higher when an oxygen concentration of a gas to be filtered is lower. The dehumidification mechanism is a pump unit including a water seal pump to provide an adiabatic expansion chamber in which the exhaust gas extracted from the fuel cell expands adiabatically.