In case a vacuum is generated in an ejector pump when compressed air is ejected into the ejector hole from the nozzle hole and air in the air intake chamber between the holes is sucked and discharged outside the chamber, the vacuum has to be broken by introducing the compressed air into the evacuated system when the operation of the pump is finished. However, the conventional method has had a disadvantage that sometimes the compressed air escapes into the atmosphere through the ejector hole so that an effective vacuum breaking operation is hindered.