A dynamic vibration absorber using a pendulum can tune its natural frequency by the length of the pendulum. However, in the case where the rotation angle of the pendulum is large, the natural frequency deviates from the optimum value because of the nonlinearity of the restoring force of the pendulum. Therefore, this paper proposes a new mechanism to reduce the nonlinearity of the dynamic vibration absorber. The pendulum length increases as the rotation angle of the pendulum increases when the proposed mechanism is used. This paper also proposes the method to reduce the number of the nonlinear terms in the equation of motions. This method makes the directions of motions of the pendulum and cart perpendicular. The effectiveness of the proposed methods and theoretical analysis is verified through simulations and experiments.