To overcome the disadvantage of a conventional drier wherein material to be treated sticks to the wall surface of a treatment vessel or the material to be treated becomes hard in a part where stirring is incompletely performed to cause unequal drying degree and lowering of thermal conductivity and to solve problems wherein scattered material scattering in the treatment vessel is discharged from an exhaust port and the scattered material stays in a vacuum pump or a heat exchanger.

In the reduced-pressure drier 10, in the treatment vessel 12 including a blade body 20 and having an atmosphere under reduced pressure, the material to be treated is stirred and heated, and the gas generated from the material to be treated is forcibly discharged from the treatment vessel 12 to dry and crush the material to be treated. The treatment vessel 12 is made cylindrical with both ends closed, a connecting part between the peripheral surface of the cylinder and closed surface is chamfered and the closed surface is made spherical. The exhaust port 12c for discharging gas from the treatment vessel 12 is provided with a scattering material returning unit 27 constructed by arranging side by side a plurality of angled plate-like bodies.

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