TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Conditions: The amount of feed material to be supplied to the reformer is not increased when the detected temperature is lower than the reference temperature, and the amount of feed material is increased when the detected temperature is at least equal to the reference temperature.    TECHNOLOGY FOCUS - MECHANICAL ENGINEERING - Preferred Device: The hydrogen generator comprises a controller, and an oxidation-gas supplying unit to supply oxidation gas to the CO-reducing unit. The controller performs control operations so that: (i) the detected temperature reaches a temperature at least equal to the reference temperature when the detected temperature is lower than the reference temperature, (ii) the amount of feed material is increased when the detected temperature reaches the temperature at least equal to the reference temperature, (iii) heating calories in the heater is increased to raise the detected temperature to a temperature at least equal to the reference temperature when the detected temperature is lower than the reference temperature, (iv) water to be supplied to the reformer is reduced in an amount to raise the detected temperature to a temperature at least equal to the reference temperature when the detected temperature is lower than the reference temperature; and (v) the oxidation gas is supplied to the CO-reducing unit to raise the detected temperature to a temperature at least equal to the reference temperature when the detected temperature is lower than the reference temperature. The CO-reducing unit is a shifter or a selective oxidation unit.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Catalyst: The CO-reducing catalyst is a shift catalyst to progress a water-gas shift reaction through which hydrogen and carbon dioxide (CO2) are generated from CO and water, or a CO selective oxidation catalyst to subject CO to selective oxidation reaction. The shift catalyst includes a catalytic body comprising noble metal and metallic oxide of cerium, zirconium, and/or aluminum.