PURPOSE: To improve the thermal efficiency by providing a combustion chamber, a regenerator, a mixing chamber, a catalyst chamber, and a boiler chamber in series from the lower part to the upper part in a plurality of reformers.

CONSTITUTION: A fuel (b) and air (d) where the latter is sent through a pressure pump 35, a tank 36, and a flowmeter 37 are fed into a combustion chamber 4 of reformers 1, 2 and burned. The generated combustion gas (e) is allowed to rise into a regenerator 5 to heat a heat storage material 12, sent through a mixing chamber 6, sent to a catalyst chamber 7 to heat a catalyst 15 to 700-900°C and remove adherent substances, sent to a boiler chamber 8 to generate steam C by means of a water tube boiler 16, and then sent to a waste heat boiler 31 to generate steam C. Then the feeding of the fuel (b) and the air (d) is stopped, and the steam C is sent to the chamber 4 to expel the combustion gas (e), and the steam C is introduced into the regenerator 5 to generate a high temperature steam (g). The high temperature steam (g) is introduced into the chamber 6, where it is mixed with a raw material (a) fed through a flowmeter 22 and heaters 23, 24, and the mixture is introduced into the chamber 7 to cause reaction, thus generating a reformed gas (h). The gas (h) is sent through the chamber 8 into a CO converter 9, where it is modified with CO to produce town gas (i). The town gas (i) is sent through heaters 23, 24, a cooler 55, and a dehydrator 57 into a tank for storing.