This paper deals with the optimum design of the torsional elastic hinge instead of the flexure hinge used as the revolutionary joint of the precise mechanism. Influence of the torsion beam dimensions on the flexural stiffness and torsional compliance of the hinge is investigated by using the finite element method, and the stiffness is compared with that of the conventional circular notched flexure hinge. As a result, the torsional hinge with the same stiffness as the flexure hinge has several times higher rotational angle under a maximum stress constraint condition. A displacement amplifier with the torsional hinge shows that the measured stiffness agrees with the calculated result, and the magnifying efficiency is 86%. By notching to the torsion beam center, the ratio of the flexural stiffness to the torsional stiffness has increased 55%, and the rotational angle has increased 19%.