To provide a heat treatment furnace improved in heat treatment quality while reducing a heat energy loss compared to a conventional one to make effective use of heat.

In this rotary heat treatment furnace 3, a powder and granular material is filled in a furnace body 39 and heated by hot air blown out of a hot air pipe, to flow to thereby form a fluidized layer 13, and a workpiece 11 made of metal is rotated in the fluidized layer by a workpiece conveying means and heat-treated. In the rotary heat treatment furnace 3, the hot air pipe has a plurality of header pipes 34 each provided with a plurality of dispersion pipes 35. The plurality of header pipes 34 respectively present divided ring shape and constitute one ring as a whole. The plurality of dispersion pipes 35 present elongated cylindrical shape on the whole having a large number of nozzles or pores for blowing off hot air and are arranged horizontally toward the center of one ring from the side face of the header pipe 34.