PURPOSE: To prevent hunting of pump start/stop by acquiring drive combination of a pump from a water level of the pump and a discharge flow rate of the pump, estimating an inflow flow rate and controlling discharge valve opening so that the current inflow flow rate is contained in a pump total discharge flow rate range after changing at the time of changing combination of the drive pump.

CONSTITUTION: This pump control device 11 inputs signals of a level gauge 7 and a discharge flow meter 10 and a discharge valve opening signal of a pump group 5 to a process input output processing part 11A, outputs commands of start/stop of a pump, speed control and discharge valve opening control, and a pump control means 11D acquires drive combination of the pump and controls it. By enumerating and computing a discharge valve opening target value matched to an inflow flow rate the estimated value after additional start or additional stop of the pump, the pump is controlled so that an inflow flow rate is contained in a pump total discharge flow range, and consequently, it is possible to carry out automatic control without generating hunting of the pump start/stop.