A turbo-molecular pump of high safety and reliability has been developed so that if an abnormal condition should develop on the rotor structure, it will not lead to damage to the stator or pump casing to cause loss of vacuum in a vacuum processing system. The turbo-molecular pump comprises a pump casing housing a stator and a rotor therein, a vane pumping section and/or a groove pumping section comprised by the stator and the rotor, and a constriction releasing structure for releasing constriction of at least a part of the stator when an abnormal torque is applied to the stator by the rotor.