This paper proposes vibration control of resonant system by using reflected wave rejection without sensing load position. In a conventional research, a vibration control using reflected wave rejection and wave compensator that is based on wave equation was proposed. The conventional method can suppress the all resonances which resonant system has because resonant system is modeled as wave equation. However, the conventional reflected wave rejection needs sensing a load position. In this paper, a novel reflected wave rejection is proposed. The reflected wave rejection method is based on a reaction force estimated by a reaction force observer. The reaction force observer uses only motor side information. The effectiveness of proposal is equivalent to that of conventional method, but the proposal is superior than the conventional method in term of no using load position information. Finally, the validity of the proposed method is verified by the experimental results.