PURPOSE: To control flow rate reasonably by an arrangement which assures low cost by coupling the middle parts between a check valve and a gate value of each pump using a connecting pipe having line resistance.

CONSTITUTION: The middle parts of check valves 17, 18, 19 gate valves 20, 21, 22, respectively, installed at the discharge sides of pumps 11, 12, 13 are coupled together using connecting pipes 27, 29 provided with restrictors 28, 29, respectively. According to this constitution, water can be delivered to a water delivery pipe 26 through a connecting pipe only by operating the gate valves 20W22 from fully open to fully closed and vice versa, so that rate of flow can be reasonably controlled by an arrangement which does not require much cost.