A thermal processing apparatus including: a cylindrical processing vessel; a support unit to be loaded into and unloaded from the vessel; and a heating furnace surrounding an outer periphery of the vessel, with a cooling space therebetween. The furnace is connected to a cooling-gas introduction unit, including a gas introduction passage to which a blowing fan is connected, for introducing a cooling gas into the cooling space during a temperature lowering operation after a thermal process. The furnace is connected to a cooling-gas discharge unit, including a heat exchanger, a suction fan, and a gas discharge passage, for discharging the cooling gas of a raised temperature from the cooling space. Connected to the gas discharge passage at a position upstream of the heat exchanger is a temperature-lowering gas introduction unit for introducing a temperature-lowering gas to the cooling gas of a raised temperature so as to lower its temperature.