PURPOSE: To produce hydrogen at low cost and high reaction rate at low temp. with a small apparatus without requiring a separation stage by using hydrocarbons for a source of H2 and carrying out generating reaction of H2 in a reaction chamber constructed with an H2-permselective material for a part of the partition wall.

CONSTITUTION: A reaction chamber A is constituted of an external pipe 1 having an internal pipe 2 consisting of an H2-permselective material having a catalyst supporting plate 5 at the bottom and consisting primarily of SiC, Si3N4, or SiCN, etc., and having 1W15% porosity, permitting its internal space to function as a hydrogen separating chamber B, and packing a catalyst 10 between the internal wall of the external pipe 1 and the external wall of the internal pipe 2. Hydrocarbons for the H2 source and steam are introduced through a gas introducing pipe 3, and allowed to react by heating the reaction chamber A from outside in a heating furnace, etc. H2 in the reaction product is permeated through the H2-permselective material which constructs the pipe wall of the internal pipe 2 and transferred to the H2 separating chamber B, and discharged to the outside through a gaseous H2 discharging pipe 6. On one hand, by-products such as CO, CO2, etc., in the reaction chamber are discharged from a discharging pipe 4.