A protective device is provided for protecting a turbo molecular pump having a rotor mounted for undergoing rotation, an intake port for sucking gas by rotation of the rotor, and an exhaust port for exhausting the gas sucked from the intake port. The protective device has a detecting device for detecting the occurrence of an abnormal phenomenon in the turbo molecular pump. An abnormal phenomenon inference device infers a type of the abnormal phenomenon detected by the detecting device. A value obtaining device infers a magnitude of damage given to the turbo molecular pump by the abnormal phenomenon inferred by the abnormal phenomenon inference device and obtains a value weighted based on the inferred magnitude of the damage. A value accumulation device accumulates the value obtained by the value obtaining device. A sum obtaining device obtains a sum of the values accumulated in the value accumulation device. A protecting device protects the turbo molecular pump in a case where the sum obtained by the sum obtaining device exceeds a predetermined value.