NOVELTY - A stop method of hydrogen production apparatus involves purging with steam flow path including modification catalyst, shift reaction catalyst and selective-oxidation catalyst, blocking flow path from external field, and introducing air into flow path from downstream of shift catalyst in order to eliminate negative pressure of flow path.    USE - A stop method of hydrogen production apparatus for fuel cell system used as home-use small power supply.    ADVANTAGE - The method is safe, economical and easy, and suppresses catalyst deterioration without integrating automatic opening-closing valve of nitrogen gas cylinder, purge gas mechanism or negative-pressure compatibility.    DETAILED DESCRIPTION - A stop method of hydrogen production apparatus involves purging with steam flow path including modification catalyst, shift reaction catalyst and selective-oxidation catalyst, blocking flow path from external field, and introducing air into flow path from downstream of shift catalyst in order to eliminate negative pressure of flow path. The temperature of shift catalyst is less than or equal to 40 degrees C. The hydrogen production apparatus comprises modifier (7) provided with modification catalyst which can accelerate modification reaction which obtains gas which contains hydrogen using modification reaction from raw material for hydrogen production, shift reaction device provided with shift catalyst which can accelerate shift reaction which reduces carbon monoxide concentration in outlet gas of modifier by shift reaction, and selective-oxidation reactor (11) provided with selective-oxidation catalyst which can accelerate selective-oxidation reaction of reducing carbon monoxide concentration in outlet gas of shift reaction device by selective-oxidation reaction which selectively oxidizes carbon monoxide. An INDEPENDENT CLAIM is included for a stop method of fuel cell system.    DESCRIPTION OF DRAWING(S) - The drawing shows a flowchart of fuel cell system.    Water tank (1)    Water pump (2)    Fuel tank (3)    Modifier (7)    Selective-oxidation reactor (11)