Patent ID: 8459931

Claim:
A turbo-molecular pump comprising: a blade pumping section having a plurality of rotary blades and a plurality of stationary blades which are alternately arranged in plural stages along an axial direction of said pump; and a drag pumping section having a cylindrical-shaped stator member, and a rotary cylinder adapted to be rotated inside said stator member, wherein said rotary cylinder has a downstream edge located on an upstream side relative to a downstream edge of said stator member with respect to said axial direction, and a relationship t≧b×h/a is satisfied, wherein “t” is a distance between respective lower edge surfaces of said stator member and said rotary cylinder in the axial direction of the pump, “a” is a distance between a distal end of a discharge port and an inner peripheral surface of said stator member in a radial direction of said pump, “b” is a distance between an inner peripheral surface of said rotary cylinder and said inner peripheral surface of said stator member in the radial direction of the pump, and “h” is a distance between a bottom of said discharge port and a lower edge surface of said stator member in the axial direction of said pump.