PURPOSE: To feed sand or the like to a classifier with consumption of small energy without using any conveyor or the like, by forming a sand pump movably up and down and turnably, drawing granular materials, such as sand, together with water, and removing foreign matters in a hopper immediately before the classifier.

CONSTITUTION: A hopper 1 is instaled immediately before the feed water inlet M1 of a classifier M. A sand pump 4 connected with the hopper 1 is moved up and down and turned using a winch 7 or the like to move sand or the like granular materials piled up on the ground. Water is fed to granular materials S, powder material S are drawn together with water through a flexible pipe 32, and delivered to the inlet 11 of the hopper 1 from a lifting vertical pipe 3. The fluid mixed with the granular material S is passed through a removing device 2, such as filter or brush, installed in the hopper 1 to remove roots, broken branches, bulky refuse, stones, and the like foreign matters, and the fluid is fed into the classifier M to classify the powder materials S into desired grain sizes. The exhausted muddy water is returned to near the pump 4 through a recirculartion pipe M6 to use it as part of replenishing water.