PURPOSE: To simplify nozzle machining by making the bottom plate of fluidized bed as a flat plate, providing plural nozzles in the plate directed in the direction of flowing medium rotation and inclined to the plate surface and using the plate of thickness over three times the diameter of the nozzles.

CONSTITUTION: Under a rotating jet flow furnace 1, an air chamber 2 is provided and its upper surface forms a multi-hole plate 3 which is the flat bottom plate of the furnace 1, and compressed air blowing out from many nozzles 4 made in the multi- hole plate 3 forms a fluidized bed 7. In the center of the multi-hole plate 3, an air jet pipe 5 is provided to generate circular flow 6 in the fluidized bed 7. The center lines of the nozzles 4 are inclined to the plate surface by angles α and the angle α of nozzles on a virtual circle 81 near the outer periphery is made smaller than that on a virtual circle 84 near the center to make turning force stronger. If the diameter of the nozzles 4 is d and the thickness of the plate is t, it is most desirable to use a value in the range t>3d for machining and forming the rotating jet flow.