An apparatus and method of generating a carburizing atmosphere stably generate a reformed gas containing carbon monoxide of high concentration that is suitably used as a carburizing atmosphere. A first reforming furnace and a second reforming furnace are connected in series. A first cooler that removes moisture in an intermediate reformed gas from the first reforming furnace and a hydrocarbon adding section that adds hydrocarbon to the intermediate reformed gas are disposed between the first and second reforming furnaces. A raw material mixed gas with a low mixture ratio of hydrocarbon is introduced into the first reforming furnace to cause a catalytic reaction, thereby generating the intermediate reformed gas. Moisture contained in the intermediate reformed gas is removed. Hydrocarbon is added to the intermediate reformed gas. The intermediate reformed gas is introduced into the second reforming furnace to cause a catalytic reaction, to generate a carburizing atmosphere.