PURPOSE: To efficiently wash a material to be washed such as rice by injecting a high pressure liquid in which air is dissolved or dispersed into a transfer pipe in the transfer direction of the material to be washed to apply transfer force to the material to be washed.

CONSTITUTION: When the grain 91 in a washing container 92 is washed, high pressure water is injected toward the outflow port 120 of an L-shaped part 119 and negative pressure is generated on the side of a suction port 95 to suck the grain 91 to emit the same into the washing container 92 through an emitting orifice 96a and a supply port 111. At this time, the contaminant bonded to the surface of the grain 91 is removed by the mutual contact of the particles of the grain 91 moved through a transfer pipe 94. By dissolving or dispersing a large amt. of air in the fresh water 28 injected into the transfer pipe 94, a large amt. of fine air bubbles are generated in high pressure water when the high pressure water is moved through the transfer pipe 94 and the grain 91 is washed by ultrasonic waves generated when air bubbles are bursted. The grain 91 after washing is separated by the filter member 123a of a separator 123 to be taken out to a taking-out container.