To prevent the sticking of a rotor blade shaft arm and an arm piece at a contact surface.

A flange part 52 of a flanged bush 51 composed of self- lubricating material is extended to provide a step part 16 on the contact surface 40 of the arm piece 10 and the rotor blade shaft arm 20. The flanged bush 51 is incorporated in an arm shaft attachment hole 11 of the arm piece 10 and the flange part 52 of the flanged bush 51 extends out to the step part 16 of the arm piece 10. Since the thickness of the extended flange part 52 is larger than the depth of the step part 16 of the arm piece 10, the flange part 52 gets into contact with the rotor blade shaft arm 20. Since friction resistance between the rotor blade shaft arm 20 and the arm piece 10 is greatly reduced and wear is almost eliminated with this kind of structure, the sticking of the arm piece 10 and the rotor blade shaft arm 20 is prevented even if both of those slide during rotor blade pitch change.