To obtain a vacuum pump apparatus which reduces noise caused by bubble bursts in the apparatus, and prevents generation of a water hammer phenomenon generated inside an ejector upon stopping a circulation pump.

A diffuser 7 of an ejector 1 is placed and attached inside a tank 2. An air communicating tube 9 is fitted at the lower portion of a divergent portion of the diffuser 7. A bulkhead tube 12 is installed at the bottom inside the tank 2. Part of the lower side of the diffuser 7 is inserted into the upper inner portion of the bulkhead tube 12. Fluid sucked into an suction chamber 8 of the ejector 1 is combined with the air sucked from the communicating tube pipe 9. Thus, the combined air becomes a buffer material of noise transmission as well as a buffer material for vapor bubbles upon crushing, thus reducing noise transmission to the outside of the apparatus. Moreover, when the driving of the circulating pump 3 is stopped, the air is sucked into the ejector 1 from the communicating tube 9, thus preventing the generation of the water hammer phenomenon.