PURPOSE: To eliminate that water is injected from an air ventilating hole at the time of operation of a submergible pump so as to suppress reduction of pump efficiency, and also prevent the air ventilating hole from clogging by foreign matters, and avoid any loss of discharging function of air.

CONSTITUTION: An air ventilating hole 8 is formed on the ceiling 4A of a horizontal discharging passage 4 for coupling a casing 2 with a discharging port 5, and a plate shaped valve 9 which is rotatably in vertical direction is hinge- connected 10 to the bottom surface of the ceiling 4A positioned on the upstream side of water flow R1 in the vicinity of the air ventilating hole 8.