PURPOSE: To enable priming to a storage pump by the action of negative pressure generated by an ejector.

CONSTITUTION: An ejector 1 is provided, and high pressure air for a plant is led into the ejector 1 and jetted from a nozzle 12 to generate negative pressure to a suction port 11. This negative pressure is led into a storage pump 91 through a negative pressure passage 83 and the like. A drain passage 82 is provided branching off from the intermediate part of the negative pressure passage 83, and motor-driven valves 51, 52, 53, 95 are provided at the intermediate part of the drain passage, or the intermediate part of the negative pressure passage 83, and further at the intermediate part of a discharge pipeline 81, and the like. A level sensor 3 is provided at the intermediate part of the drain passage 82, and a control means 2 is provided to control these motor-driven valves, never sensor 3, an electric motor 93 for driving the storage pump 91, and the like. When priming is pumped up to the storage pump 91 by the action of negative pressure, the control means 2 actuates the electric motor 93 by a signal from the level sensor 3 so as to put the storage pump 91 in operation and to stop the operation of the ejector 1 and the like.