HYDROGEN GENERATING APPARATUS, FUEL CELL SYSTEM, AND METHODS OF OPERATING THEM

A hydrogen generating apparatus includes a reformer generating hydrogen-containing gas through a reforming reaction, a raw material supplier supplying a raw material to the reformer, a reaction gas supplier supplying reaction gas other than the raw material to the reformer, a hydro-desulfurizer removing a sulfur compound in the raw material supplied to the reformer, a recycle flow passage through which part of the hydrogen-containing gas generated by the reformer is supplied to the hydro-desulfurizer, a closing device that closes the recycle flow passage, and a controller that, when stopping operation, closes the closing device and controls the raw material supplier and the reaction gas supplier such that the raw material and the reaction gas are supplied to the reformer, before a temperature of the reformer drops down to a temperature at which deposition of carbon from the raw material on a reformation catalyst disposed inside the reformer is suppressed.