PURPOSE: To prevent the occurrence of crimp and whirling between female and male shafts regardless of the relative elongation quantities of both shafts by partitioning and forming hydraulic pressure chambers extending in the peripheral direction on the outer periphery of an annular bush, and connecting the hydraulic pressure chambers to a hydraulic pressure supply means through a hydraulic pressure path.

CONSTITUTION: When properly selecting relative positions in the axial line directions of both female and male shafts 2 and 1 under the action of the spring force of a spring 5 or against the spring force, an annular bush 11 is swelled out and deformed in the radius direction over its whole periphery preferably, and comes into close and uniform contact with the outer periphery of a male shaft 1 by supplying a hydraulic pressure to respective hydraulic pressure chambers 13 from a hydraulic pressure means. Therefore, a gap between the male shaft 1 and the annular bush 11 is sufficiently removed. Also, since the male shaft 1 is held by a desired hydraulic pressure, both female and male shafts are always kept on the same axial line, so that crimp is not caused between both shafts.