The use of wind turbine generator has rapidly spread as a one of the foremost clean energy sources. Recently, as the size of the wind turbine generator has become larger, its maintenance has become more difficult. However, there are few studies on the vibration analysis and its suppression in the conventional researches. The wind turbine is a special type of rotating machinery which has a long heavy blade rotating in the vertical plane under the action of the gravitational force. The wind power acting on the wind turbine blade varies periodically because of the height-dependent characteristic of the wind. Therefore, the dynamical design and analysis of the wind turbine blade requires a more thorough study. This paper investigates the fundamental vibration characteristic of an elastic blade of the wind turbine. The nonlinear vibration analysis of the superharmonic resonance is performed, and its characteristics are explained. Furthermore, the effect of the interaction of both the gravitational force and the wind force on the superharmonic resonance is clarified.