PURPOSE: To economically generate a gaseous mixture consisting essentially of H2 in high yield by controlling the high-temp. part and low-temp. part of a reformer to an appropriate temp.

CONSTITUTION: The methanol and water from pumps 2 and 4 are mixed, and the mixture is introduced into a heat exchanger 30 and heated by heating- medium oil flowing in a heat-transfer pipe 31 at a preheating part 30a to a temp. close to the b.p. The mixture is then evaporated at an evaporating part 30b, heated at a superheating part 30c, and supplied to the reformer 33. The gaseous mixture is passed through a reformer pipe 34 packed with a catalyst, the methanol is allowed to react with water by the heating-medium oil flowing in a space 35 at a cracking part 33a, hence gaseous H2, CO2, and CO are generated, the gaseous mixture is introduced into a conversion part 33b, and CO is converted wile keeping the part 33b at a temp. lower than that of the cracking part 33a. The obtained gas consisting essentially of gaseous H2 and CO2 is introduced into a cooler 8, excess moisture is condensed therein, water is removed in a gas-liq. separator 10, and the removed water is circulated through a duct 11. Meanwhile, the gas is introduced into an adsorptive separator 12 to separate gaseous H2 which is taken out from a duct 13.