To improve the temperature detecting accuracy without using a radiation thermometer and to detect the abnormality and the like of a pump rotor securely for a rotor-temperature detector, which detects the temperature of the pump rotor as the unitary rotary body with a rotary shaft floated and supported by a magnetic bearing in a turbo-molecular pump.

This method is made to have a thermal-expansion-amount detecting means 32, which detects the amount of the thermal expansion of a pump rotor 5, and a temperature operating means, which operates the temperature of the pump rotor 5 based on the detected amount of the thermal expansion detected by the thermal-expansion-amount detecting means 32. Furthermore, the thermal-expansion-amount detecting means 32 has two contactless position sensors 31 and 31 for detecting the amount of the thermal expansion of the pump rotor 5. Both position sensors 31 and 31 are provided so as to face the axial center of the pump rotor 5 to each other.