PURPOSE: To reduce the time from the time the water level of a water absorption well reaches to the pumping starting water level to the time a drainage operation is started, so as to respond to an emergent condition, by reducing the time from the time the water level of the water absorption well reaches to the pumping starting water level to the time the water level in a pump is leveled up to the high water level.

CONSTITUTION: A check valve 10 to allow the flow in the regular direction and to shut the flow in the reverse direction is provided in a suction pipe 8 at the upstream side of an impeller 5, and a holdup member 12 to hold up the water necessary to maintain the water level in a pump at the high water level HHWL is provided to a discharge pipe 11 at the downstream side of the impeller 5. And a water filling tank 13 with the capacity to fill the water in the pump to the high water level HHWL is provided, and when the water level of a water absorption well 1 is raised to the pumping starting water level HWL, the water is filled in the pump from the water filling tank 13, so as to make the water level in the pump to the high water level HHWL.