PURPOSE: To properly develop sealing effect even if working fluid has a high temperature, high pressure and a high viscosity, by forming a screw groove which applies the force directed inside a casing for the fluid in a gap, on the outer periphery of a rotary shaft.

CONSTITUTION: Inside a through hole 15 on a stuffing box 7, a screw groove 53 is formed on the outer periphery of a driving shaft part 11. The direction of torsin of the screw groove 53 is the direction for applying the force directed toward the inside of a casing 2 to the fluid which tends to leak outside the casing, passing through the gap between the inner and outer peripheries of the stuffing box 7 and the driving shaft 11 by the revolution of the driving shaft 11. Accordingly, even if a portion of the fluid which lubricates the bearing part of the driving shaft 11 tends to leak outside the casing 2 from the gap between the inner and outer peripheries of the driving part 11 and the stuffing box 7, the fluid is pushed back to the inside of the casing 2 by the revolution of the screw groove 53, and the leak can be prevented.