A desulfurization unit for a fuel cell system includes a first desulfurizer arranged in a temperature environment ranging from 50° C. to 200° C. and accommodating a desulfurizing agent including a porous material serving as a base material, the desulfurizing agent exerting a desulfurization effect in a normal temperature range, the first desulfurizer adsorbing a sulfur compound included in a source gas in the temperature environment ranging from 50° C. to 200° C. when the source gas having a low dew point is supplied through a source gas passage to the first desulfurizer and when the source gas having a high dew point is supplied through the source gas passage to the first desulfurizer.