PURPOSE: To make it compact and to prevent leakage of an organosulfur compound by providing a hydrogenation catalyst layer, a first desulfurization catalyst layer, and a second desulfurization catalyst layer in order.

CONSTITUTION: When a fuel cell generator is started up, a valve 19 is closed and a valve 21 is opened to allow a reformed raw material fuel to flow through an inlet 6 of a raw material fuel supply system 7 into a desulfurizer 15. In the desulfurizer 15, the reformed raw material fuel comprising a sulfur- containing hydrocarbon fuel gas is reacted with hydrogen in a layer 1 of a Co/Mo or Ni/Mo base hydrogenation catalyst to form hydrogen sulfide; the hydrogen sulfide is adsorbed in a layer 2 of a first desulfurization catalyst of ZnO base; and the hydrocarbon gas is adsorbed in a layer 11 of a second desulfurization catalyst of CuO base or Fe base. The raw material from which the organic sulfur has been removed is sent through a branch pipe 22, with a valve 21 open, of a raw material fuel discharge system 18 to the next process.