This paper focuses on a bandwidth and a delay of force sensing. High bandwidth force sensing is important for motion control systems to cope with unknown environments. Reaction torque observer is utilized instead of force sensors to detect external force in this paper. The bandwidth of force sensing is limited by the sampling period and data noise. The delay in force information may deteriorate the performance of force control since force information is fed back. According to these considerations, this paper proposes application of a multirate sampling method to the force control system. Reaction torque observer is modified for the multirate system. The bandwidth of force sensing can be improved and the delay in force information can be decreased with the proposed method. The validity of the proposal is verified by stability analysis, simulation and experimental results.