PURPOSE: To reduce a piping part and to prevent leak of oil or air from a bearing part, by a method wherein two different pump bodies and motors are contained in an integral one-piece casing.

CONSTITUTION: An integral one-piece casing 2 of a vacuum pump 1 is provided with a first pump chamber 12, being open to a suction port 11, a second pump chamber 14, being open to a delivery port 13, an internal flow passage 15, through which the two pump chambers 12 and 14 are intercommunicated on the side reverse to the opening parts, and a motor chamber 17 being positioned adjacent to the second pump chamber 14 through a partition wall 16 and being a closed space. A motor 3 is situated in a motor chamber 17 through a seal member 19 in a manner that an output shaft 18 is extended through the partition wall 16 to the second pump chamber 14 side. The vacuum pump is provided with a pair of female and male screw rotors 5, adapted to deliver gas, sucked through an internal flow passage 15, to the delivery port 13, and on the same shaft as those of the screw rotors with an impeller 6, serving as a speed type pump body, which delivers gas, sucked through a suction port 11, to the internal flow passage 15.