The first state is a state where the third link member 33 is rotated about the rotation center C3 (axial center of the shaft portion 33c) of the third turning pair in the one direction (counterclockwise direction on the drawing) and the outer surface of the third link member 33 abuts on the first link member 29 or second link member 31 or a state where the third link member 33 is rotated by the fi