NOVELTY - Operating method of hydrogen generating apparatus (100) which involves performing step which removes sulfur compound in raw material by hydrodesulfurization device (2), performing step which produces hydrogen-containing gas with modifier (4) using raw material supplied from hydrodesulfurization device and water vapor, and performing step which carries out gas-liquid separation of condensed water produced from hydrogen-containing gas by supplying hydrodesulfurization device into recycling flow path (6) for recycling part of hydrogen-containing gas.    USE - Operating method of hydrogen generating apparatus for fuel cell system (claimed).    ADVANTAGE - Adverse effects of temperature variation of hydrogen-containing gas to be recycled to hydrodesulfurization unit can be reduced.    DETAILED DESCRIPTION - Operating method of hydrogen generating apparatus (100) which involves performing step which removes sulfur compound in raw material by hydrodesulfurization device (2), performing step which produces hydrogen-containing gas with modifier (4) using raw material supplied from hydrodesulfurization device and water vapor, and performing step which carries out gas-liquid separation of condensed water produced from hydrogen-containing gas by supplying hydrodesulfurization device into recycling flow path (6) for recycling part of hydrogen-containing gas and flowing gas in flow path in which hydrogen-containing gas is cooled after flowing gas into recycling flow path or before flowing into recycling flow path. When temperature of hydrogen-containing gas passing through gas-liquid separation is lowered, ratio of oxygen-containing gas supply volume to modifier with respect to raw material feed rate to modifier is increased and ratio of hydrogen-containing gas which flows into recycling flow path is reduced. INDEPENDENT CLAIMS are included for:    (1) hydrogen generating apparatus comprising hydrodesulfurization device, modifier, recycling flow path, gas-liquid separator (8), gas supply volume ratio regulator (10), and controller (12); and    (2) fuel cell system provided with hydrogen generating apparatus.    DESCRIPTION OF DRAWING(S) - The drawing shows a block diagram of the hydrogen generating apparatus. (Drawing includes non-English language text).    Hydrodesulfurization device (2)    Modifier (4)    Recycling flow path (6)    Gas-liquid separator (8)    Gas supply volume ratio regulator (10)    Controller (12)    Hydrogen generating apparatus (100)