PURPOSE: To automatically control driving of a rake, by a method wherein a water turbine is rotatably mounted to a member elevating due to an increase and decrease of water amount in a tank, and the runners of the water turbine are immersed in flow water resulting to rotate from lowering of the elevating member.

CONSTITUTION: When dust gathers at a screen 10, a water level at the upstream side of the screen is raised. If a difference in water level between the upstream and the downstream exceeds a fixed value, a shaft secured to a lever 88 is turned by floats 84 and 86 to open a drainage valve 89. If water in a water tank 54 decreases, the weight decreases, the water tank is raised, a water turbine 38 is lowered, it starts a dust removing work through a turn by dint of flow water, and simultaneously, water is pumped up to a tank by a pump 70. When no difference in water level is produced, a drainage valve 89 is closed, and water begins to gather in the water tank 54. If the water tank 54 is increased in weight, the water turbine 38 is raised, it stops spinning, and a dust removing work is also brought to a stop.