PURPOSE: To economically sprinkle water over a pile of powdery or granular material to prevent dust from flying, by making the quantity of the sprinkled water on and near the ridges of the top part of the pile larger than that on its lower part to control the amount of the sprinkled water depending on that of the dust.

CONSTITUTION: Different nozzles 2, 2a, 3, 3a are provided for both the sides of a pile 1 of powdery or granular material. When wind blows in a direction 4, water is sprinkled centering ridge 5 of the top part of the pile through a nozzle 2 and sprinkled over the lower part of the pile through the nozzle 3. At that time, the quantity of water sprinkled through the nozzle 2 is made larger than that through the nozzle . The pile 1 is detected of its part easy for dust to fly and its other part hard for dust to fly, from the relationship between the wind speed ratio on the surface of the pile and its surface humidity corresponding to the beginning of flying of the dust, as the pile is formed. The amount of the sprinkled water is controlled, as mentioned above, depending on the easy and hard parts of the pile. this results in reducing the amount of the sprinkled water for preventing the dust from flying.