PURPOSE: To prevent a rotary shaft from vibrating axially in a housing by furnishing a communication hole with a flow-in port, which opens from the periphery of the rotary shaft outward in the radial direction, and a flowout port which opens from the end face of the rotary shaft outward in the axial direction.

CONSTITUTION: Inside of a rotary shaft 3 is provided a communication hole 32, which leads from an upstream fluid path 21 to a downstream fluid path 22 and which is equipped with a shaft hole 33 and a radial hole 34. A flow-in port 35 is formed at the rotary shaft 3 peripheral surface of the shaft hole 33 and leads to an inlet port 27 via a bearing 4. The rotary shaft 3 is also provided with a flowout hole 36. Most water flowing into a control chamber 23 will flow out from the flowout port 36, while part of the water flows into the gap between the inside surface of a housing 2 and the periphery of the bearing 4 and also the gap between the bore of the bearing 4 and the periphery of the rotary shaft 3 so as to prevent it from vibrating in the axial direction.