TECHNOLOGY FOCUS - MECHANICAL ENGINEERING - Preferred Components: The supply portion supplies the raw material and oxygen to the reforming portion, and the hydrogen suppressing portion controls the supply portion so that a ratio of oxygen to raw material becomes greater than a value suitable for hydrogen generation when the hydrogen generating device is in the low-temperature condition.The hydrogen suppressing portion includes an oxygen supply mechanism for supplying oxygen between the reforming portion and hydrogen separating portion in the low-temperature condition, and a control portion for controlling the hydrogen suppressing portion to supply the oxygen. The hydrogen suppressing portion stops operating when the temperature of hydrogen separating portion reaches or exceeds a predetermined value.An oxygen-enriching control portion controls the supply portion and/or oxygen supply mechanism to create and oxygen-rich atmosphere in the reformed gas flow passage before separating hydrogen in the hydrogen separating portion. A purge gas supplying portion supplies purge gas to the hydrogen flow passage. The control portion also controls the purge gas supplying portion to stop supplying purge gas in the low-temperature condition or to supply the purge gas in a direction opposite the direction of flow of the reformed gas when hydrogen is separated and in the same direction as the direction of the flow of reformed gas in the low-temperature condition.The purge gas supplying portion controls a flow rate of the purge gas in accordance with a temperature of the hydrogen separating portion. A heat exchanger is provided between the reforming portion and hydrogen separating portion, and a reducing mechanism reduces calorie taken from the reformed gas by the heat exchanger in the low-temperature condition.The reducing mechanism is a bypass passage which delivers the reformed gas to bypass the heat exchanger. A hydrogen reflow passage returns part of hydrogen generated in the reforming portion to the hydrogen flow passage of hydrogen separating portion. A burning portion burns the hydrogen provided in the hydrogen reflow passage. The reflow passage is provided with heat exchanger, and the burning portion is provided with an oxidation catalyst in the heat exchanger.