NOVELTY - A hydrogen generating apparatus (100) comprises hydrodesulfurization device (1) which reacts sulfur compound in source gas with hydrogen, material supply device (2) which supplies source gas to hydrodesulfurization device, material supply flow path (3) installed between material supply device and hydrodesulfurization device, modifier (4) which produces fuel gas, fuel gas flow channel (5) which discharges fuel gas from modifier, fuel gas flow channel (5), recycle gas flow path (6), ejector (7), pressure detection unit (8), and controller (9).    USE - A hydrogen generating apparatus for fuel cell system (claimed).    ADVANTAGE - Detection of obstruction of recycle gas flow path can be reliably performed.    DETAILED DESCRIPTION - A hydrogen generating apparatus (100) comprises hydrodesulfurization device (1) which reacts sulfur compound in source gas with hydrogen and removes sulfur compound, material supply device (2) which pressurizes source gas and supplies source gas to hydrodesulfurization device, material supply flow path (3) installed between material supply device and hydrodesulfurization device, modifier (4) which produces fuel gas by reacting source gas and water vapor which passes through hydrodesulfurization device and contains hydrogen, fuel gas flow channel (5) which discharges fuel gas from modifier, recycle gas flow path (6) for mixing part of fuel gas which branches from fuel gas flow channel and is discharged from modifier with source gas which flows into material supply flow path, ejector (7) positioned at merging part of material supply flow path and recycle gas flow path, pressure detection unit (8) which detects pressure of material supply flow path, and controller (9) which reports state or abnormality of hydrogen generating apparatus or stops operation of apparatus if pressure value detected by pressure detection unit is equal to or less than 1st predetermined value. INDEPENDENT CLAIMS are included for:    (1) fuel cell system; and    (2) operating method of 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 (1)    Material supply device (2)    Material supply flow path (3)    Modifier (4)    Fuel gas flow channel (5)    Recycle gas flow path (6)    Ejector (7)    Pressure detection unit (8)    Controller (9)    Hydrogen generating apparatus (100)