A well-known control system that can reduce the adverse effects of disturbances is a disturbance observer. Whenever we apply disturbance observer, disturbance frequency should be known and constant. However, in many cases of industrial systems disturbance frequency is varied for some frequency range. Therefore, it may be difficult to reduce the adverse effect of such disturbance by use of the traditional disturbance observer. In this paper, a design method of disturbance attenuation system that can cope with the frequency variation (DOFV) is proposed. The main idea of this design method is to combine DOFV with frequency estimator that can estimate disturbance frequency in real time. Even though the proposed disturbance attenuation system is low degree and low gain controller, it has superior steady state characteristic. Numerical simulations and experiments show the usefulness of the proposed disturbance attenuation system.