TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The reaction source is a sodium borohydride solution. The gas generated in the reactor tube is hydrogen.    TECHNOLOGY FOCUS - MECHANICAL ENGINEERING - Preferred Reactor - The thermal siphon reactor and hydrogen generator further comprises an insulating layer (2) covering an external surface of the reactor tube; and a liquid absorption pad (5), which is separably attached to a lower end of the reactor tube, and absorbs a liquid reaction source and transfers the liquid reaction source to the catalyst layer. The hydrogen generator further comprises a control unit, which re-provides a reaction source provided from the reaction source container to the reaction tube, and is separably attached to a lower end of the reactor tube between the reaction source container and the reactor tube; a reaction source conduit disposed between the reaction source container and the reactor tube and comprising an open/close valve and a back flow preventing valve, where the open/close valve is positioned closer to the reaction source container than the back flow preventing valve; a gas discharge conduit connected to the product container so as to discharge the gas in the product container; and a gas-liquid separation membrane between the product container and the gas discharge conduit. Preferred Components: The reactor tube has cylindrical shape. The reaction occurring in the tube is an exothermic reaction. The catalyst layer is porous matrix or is cylindrical or cubical prism having smaller width than the reactor tube, and having space between the reactor tube and the catalyst layer forming the convection channel. The control unit comprises a bellows transferring the reaction source provided from the reaction source container to the reactor tube; and a liquid absorption pad, which is separably attached to a lower end of the reactor tube, and absorbs a liquid reaction source and transfers the absorbed liquid reaction source to the catalyst layer, where in the bellows expands or contracts according to the pressure of the reactor tube so that the liquid absorption pad is attached to or separated from the lower end of the reactor tube. The reaction source container is an inner space of the housing. The reaction source container and the product containers are formed of a flexible film and are separably built in the housing.