To provide efficient disposition per unit area when composing an oven furnace of a plurality of stages, and to efficiently perform baking operation etc., for a material to be processed.

There is provided a structure of a plurality of stages in which the plurality of stages are stacked through an intermediate stand 41 when composing the oven furnace 1 of the plurality of stages. An air supply mechanism 40 is provided in the intermediate stand 41. The air supply mechanism 40 is obtained by forming an air supply duct part 42 communicating with the bottom of the oven furnace 1 and the exterior of the lateral side of the intermediate stand 41, respectively; and boring an air supply hole 43 communicating with the exterior and introducing the outside air into the air supply duct 42 in the sidewall of the intermediate stand 41, and an air supply hole 44 communicating with the bottom of the oven furnace 1, and supplying supply air in the air supply duct 42 into the oven furnace 1 in the bottom wall of the oven furnace 1, respectively.