To prevent advance of air toward a pump so as to prevent falling of water by arranging a closing valve for shutting out flow of air reserved in a delivery pipe side when a delivery valve is opened, in a direction perpendicular to a flow passage.

At a time when a pump 1 is started to reach delivery pressure which is necessary for forming siphon action, a part of air rested in a delivery pipe 3 when water makes flow from a clearance of a valve element 10 into a delivery pipe 3 by opening a delivery valve 4, flows in a reverse direction from the clearance of the valve element 10. A flow passage is closed by a close plate 12 whose vertical direction length is about from 1/4 to 1/2 of a piping diameter and width of a horizontal direction is a pipe diameter or more, and thereby, reverse flow of air is obstructed so as to stay air to a downstream side of the close plate 12. After that, when a flow rate of water is increased as an opening of the delivery valve 4 is opened largely, the flow rate of water is increased more than a reverse flow rate of air, and thereby, air is finally pushed out by flow of water so as to form a siphon water passage.