A one piece shaft which supports two rotatable members is provided with shafts for energizing the rotation and for controlling an energized force of each member separately. The shaft includes a shaft body which connects two hollow shaft bodies attached to each rotatable member unrotatably on the same central shaft axis so as to rotate relatively, two members attached unrotatably to the fixed member attached rotatably to both sides of this shaft, and two torsion bars bridged between the separated hollow shaft bodies and the cap member respectively. The shaft makes possible providing the initial torque to each torsion bar at the assembling time of the shaft by being provided with a latching projection formed on one hollow shaft body, projections for stopping the rotation formed on both cap members and a latching pawl formed on the other hollow shaft body, and it is possible to prevent problems with respect to the rotation of the rotatable member and a rotation more than a range of the normal rotation by the shaft itself.
