To completely wash even the whole screw blade without leaving a part on the rear side of the screw blade unwashed in a washer used in washing of a powder agitator in which the screw blade is subjected to revolution and rotation to agitate a lot of powder such as medical supplies in a closed tank.

On washing, an introducing pipe 30 is hermetically inserted into a closed tank 15 and is hung. The introducing pipe 30 is provided with a plurality of spray nozzles 35. The spray nozzles 35 each is provided with a sector jet of an opening angle of 60° in the end surface part thereof, and is installed with the installing angle of the jet regulated so that on jetting, a spray pattern P of washing liquid has a planar shape whose side face shape is gradually widened toward the screw blade 20 and has a hemi-sector shape in which the lower side of the spray pattern P is made almost horizontal, and also the nozzles 35 are arranged in series with such intervals that the upper and lower sides of the spray patterns vertically adjacent to each other are crossed near the axial line of the screw blade 20.