A turbo molecular pump includes a magnetic bearing system which includes a rotor having an impeller connected to a shaft and a motor. A stator is positioned between the shaft and the impeller. Radial magnetic bearings, an active axial magnetic bearing and emergency bearings are each provided between the rotor and the stator. The radial magnetic bearings include passive magnetic bearings provided on the rotor and the stator respectively. The axial magnet bearing is disposed in the vicinity where the impeller is connected to the shaft. The emergency bearings are disposed on a low vacuum side with one emergency bearing being positioned near the axial magnetic bearing. A diameter of the shaft is made smaller than an inside diameter of the emergency bearing near the axial magnetic bearing. By this arrangement, only one control axis is necessary for controlling the position of the rotor. Disassembling of the shaft and impeller is easy and contamination of the high vacuum side can be prevented.