PURPOSE: To prevent a feed pump from being continuously operated caused by a leak by providing a feed pump on the inlet piping of a water storage tank to detect the water level in the storage tank, providing a valve and a flowmeter on the outlet piping of the storage tank, and controlling the opening and closing of the feed pump on the basis of the integrated value obtained from the flowmeter.

CONSTITUTION: The time for normally filling a water storage tank 2 by a feed pump 1 and the flow rate from feed level to stop level are initially inputted to a control device 4. When the feed level condition is satisfied, a valve 7 is closed, and the feed pump 1 is operated to supply water to the water storage tank 2. The operating time is integrated simultaneously with the operation of the feed pump 1. When the condition of the time for filling the water storage tank 2 ≥ the operating time of the feed pump 1 is not established before the stop level condition is satisfied, a leak is alarmed. When the stop level condition is satisfied, the feed pump 1 i stopped, and the valve 7 is opened, The outlet flow rate is also integrated, and when the condition of the flow rate from feed level to stop level ≥ the outlet flow rate integrated by a flowmeter 6 is not established when the feed level condition is satisfied, the leak is alarmed.