<p>A protrusion (21b) is formed in the central region on the inner surface (21c) of a first disc plate (21) constituting the end part on the oblique downward side of a rotary drum (2). Powder (11) in the vicinity of the other end (first disc plate (21)) lifted forward in the rotational direction as the rotary drum (2) rotates comes in contact with the surface of the protrusion (21b) when the powder flows gravitationally backward in the rotational direction. The powder then flows obliquely upward while being guided by the surface of the protrusion (21b). Consequently, stagnation phenomenon of the powder (11) is less likely to occur in the vicinity of the other end (first disc plate (21)).</p>
