PURPOSE: To control velocity of a pump through a PID adjuster, for determining a fixed aimed level for the water level of a pump well, and make improvement in that the pump velocity cannot follow abrupt rising of the water level, in a raindrop pump field gathering water in the pump well into which raindrops flow from a reservoir and delivering the water into the river and so on through the pump.

CONSTITUTION: An aimed water level corrected value l correspondent to the rising velocity of the water level of a pump well is calculated through an aimed water level corrected value calculation means 11 per a predetermined cycle, and a present aimed water level SV (t), for which the corrected value lis added to a previous aimed water level SV (t-t), is given to a pump control system. When the velocity of rising water level is larger than this level, the absolute value of a deviation of water level SV-PV is increased, and the pump velocity is increased faster accordingly.