PURPOSE: To provide an inexpensive vacuum pump system for a multi-stage gas inlet system easily operated, requiring only a narrow occupying area and operated efficiently for a gas analyzer.

CONSTITUTION: This pump system is composed of a turbomolecular pump 5, and one or more of pumps 6 arranged in a down-stream of the pump 5, and rotors of the pumps 6 are located on the same shaft as a rotor of the pump 5. An additional dry running pump 8 for conducting discharge against atmospheric pressure is operated intermittently. Inlet connection ports 9 are provided between the pumps 6. The intermittent operation of the pump 8 for conducting the discharge against atmospheric pressure is controlled depending on a current or an output of a drive motor of the first pump unit 4.