Various types of active control systems have been proposed in order to reduce wind-induced structural vibrations. The objectives of this control are to keep structures safe from some distorting damages and to avoid sea sick of habitants. The typical type of those kinds of systems is so-called active mass damper system (AMD). This system aims to use controllable inertia forces of the AMD in order to reduce the structural vibrations. However, another problem may be arisen on the AMD systems. It is that dead loads of structures obviously increased by introducing this system. Moreover, the AMD system needs large electric power to shake its additional mass. In order to solve those problems, an active fin system(1,(2)) is proposed by authors as an effective technique of the active control for wind-induced structural vibrations. The concept of this system is based on an idea to use wind force itself as effective damping forces. By changing the angle of the fin according to both wind direction and structural vibration direction, wind resistant forces can be generated arbitrarily. Moreover, the active fin system requires comparatively less electric power than that of the AMD system. In this paper, the effectiveness of two different types of control devices of the active fin are investigated by experimental tests (a wind tunnel is used for this aim). One is a single-fin type and the other is a twin-fin type. Following three items are focused to investigate: (1) Composition of an effective control algorithm for the active fin system, (2) Comparisons of control effects in the case of using the single-fin type and in the case of using the twin-fins type, (3) Estimation for real wind resistance forces acting on the fins.