PURPOSE: To prevent the penetration of exhaust gas to the side of a motor room and the corrosion of a magnetic bearing, respectively, by forming a circular chamber in the middle between the eddy current type pump element on the lowermost stage and the motor room, and making this communicate with the eddy current type pump element and the motor room through a circular gap.

CONSTITUTION: For the pump main body, an eddy current type pump element 3, which performs the exhaust in circumferential direction, is arranged at the pump stage at the lowermost stage connected to the exhaust port 92 of a housing 9. On the other hand, the rotor part interlocking with a motor 4 is supported floatingly through a magnetic bearing 5. In this case, a circular chamber 6, which surrounds the large diameter part 42 of a drive shaft 41, is made in a partition plate 95, which partitions the middle part between the eddy current pump element 3 and a motor chamber 40. And, the upper part in axial direction of the circular chamber 6 is made to communicate with the eddy current type pump element 3 through a minute circular gap 61, which surrounds the periphery of the large diameter part 42. Moreover, likewise the lower part in axial direction of the circular chamber 6 is made to communicate with the motor room 40 through a minute chamber 62, which surrounds the periphery of the large diameter part 42.