PURPOSE: To reduce the fluctuation of supply water pressure at the pump selecting time by selectively controlling the operation of plural booster pumps on the basis of the discharge side supply water pressure in both booster pumps and the operation command of a 24-hour timer for setting the operation time of both booster pumps.

CONSTITUTION: A large capacity booster pump 7 for boosting supply water pressure, and a small capacity booster pump 8 for regulating the supply water pressure are installed being parallel-connected in a water-supply distributing water pumping place. In this case, the supply water pressure on the discharge side of both booster pumps 7, 8 is measured by a pressure gauge 5, and the operating time of both booster pumps 7, 8 in a day is set by a 24-hour timer 2. The pressure signal of the pressure gauge 5 and the operation command of the 24-hour timer 2 are further compared to each other, and the operation of the booster pumps 7, 8 is selected by a pump selecting circuit 3. At this time, the selection is made according to whether the detection value of the pressure gauge 5 has become lower or higher than the set value. The operation of the booster pumps 7, 8 is then controlled by a control circuit 6 according to the operation signal of the pump selecting circuit 3.