As an approach to the experimental study of various unsteady forces acting on a hydrofoil with cavitation, we have designed a torsional vibration apparatus for a cavitating hydrofoil. The system has a driving part producing sine wave vibration, and two multicomponent load cells for measuring the unsteady fluid forces and canceling the mechanical inertia forces. This paper reports the mechanical and measuring accuracies of the system for future experimental studies and, for example, refers to various steady and unsteady fluid forces in noncavitating or cavitating flow.