Fuel cell system comprising impurity adsorbing means for adsorption of impurities contained in oxidation gas fed to fuel cell; impurity emitting means for emission of impurities adsorbed by the impurity adsorbing means from the impurity adsorbing means; impurity outlet passage for pass of impurities emitted from the impurity emitting means; and diluting means for dilution of the impurities emitted by the impurity emitting means, so that any adsorbed impurities are diluted by the diluting means before emission outside the system. Consequently, not only can impurities contained in the oxidation gas fed to fuel cell be effectively removed but also before emission of the removed impurities, there can be conducted lowering of influence on human health and environment.