To provide a highly reliable atmosphere baking furnace provided with gas displacement chambers at an inlet and an outlet of a baking furnace body, enabling smooth operation of a door causing no abnormal noise nor failure of the operation of the door when opening the door of the gas displacement chamber.

In the atmosphere baking furnace provided with the gas displacement chambers at the inlet and outlet of the baking furnace, in order to have a highly reliable door opening and closing structure enabling the smooth operation of the door causing no abnormal noise nor failure of the operation of the door when opening the door of the gas displacement chamber, pipes are arranged between an inside of the baking furnace body and the gas displacement chamber, and a valve is provided. Before opening an intermediate door, the valve is opened to have the pressure in the baking furnace body the same as that in the gas displacement chamber.