PURPOSE: To improve efficiency of heat transfer by making one face of a reaction tube into a catalyst and packing a methanol reforming catalyst to conduct a reforming reaction.

CONSTITUTION: A composite oxide of Cu and Ni is thermally sprayed on the other face 2 of a reaction tube 1 having 20-40mm diameter to make the outer face into a catalyst, a methanol reforming catalyst 3 consisting essentially of Cu, Zn, etc., is packed between the tubes, and the packed bed is used as a gaseous reactant passage 4. A heating gas or a heating medium is circulated through the heating-part passage 5 of the reaction tube 1 of the externally heated tubular reactor. A specified amt. of methanol or a mixture of methanol and water is then supplied as the raw material to the passage 5 of the reaction tube 1, heated to a reaction temp. and reformed to obtain a gas contg. ≥50mol% H2 and the balance CO, CO2 and water with high methanol conversion efficiency.