In this study, the design of controllers for the master-slave system is discussed on the basis of the H/sub /spl infin//-optimal control theory. A few controllers that achieve given performance specifications for the free motion and the constrained motion are designed in order. Especially, by considering a variation of time delay, a time-varying controller incorporates to adjust to the current time delay is designed in the framework of the gain scheduling. This control strategy typically achieves higher performance in the face of large variations in operating conditions. The effectiveness of proposed method is confirmed by the experiments and the simulations.