PURPOSE: To improve durability by forming a tubular ring by braiding a fiber reinforced composite material having fibers extended in the circumferential direction and inclined fibers orientated at a designated angle thereto, and installing a driving shaft fitting arm extended inward in the radial direction in the tubular ring.

CONSTITUTION: A braided tubur laring 3 includes a triaxially braided composite material having circumferential fibers 9 and inclined fibers 12 orientated about 30-60 degrees thereto and interwoven with the fibers 9. The resin is impregnated and hardened. Plural arms extended inward in the radial direction are fitted to the tubular ring 3 and fitted to a driving shaft. By this constitution, a retention plate withstands forces both in the directions along the plane and normal to the plane.