and lower portions of the thread stator 7 whereby heat conduction is effected actively in the stator blades 5 in the upper portion and the gas outlet 9 in the lower portion of the pump case 1 thereby reducing as much as possible the variation in temperature in the evacuation gas passage in the pump and uniformly heating the entire thread stator 7 next the inner construction of the rotor 2 will be described inside the rotor 2 a rotor shaft 11 is integrally mounted so as to be in the rotation axis thereof various types of bearing may be adopted as a bearing means of this rotor shaft 11 in this embodiment the rotor shaft 11 is supported by ball bearings 12 the rotor shaft 11 is rotated by a driving motor 13 the driving motor 13 is constituted by a motor stator 13 a mounted to a stator column 14 installed inside the rotor 2 and a motor rotor 13 b arranged on the outer peripheral surface of the rotor shaft 11 so as to be opposed to the motor stator 13 a as shown in fig2 the gas inlet 3 in the upper portion of the pump case.