Abstract—This paper deals with the control problem of a series elastic actuator (SEA) which can realize a muscle strengthening robot at low cost. We designed and fabricated SEA with improved structure and designed robust controller for it. The robust controller implements the state feedback controller without the effect of disturbance by using the integral sliding mode control(ISMC) with the state feedback controller as a nominal controller. At the same time, by adding a disturbance observer, it can cope with the larger range of disturbance, and the chattering phenomenon is reduced by decreasing the gain of the variable control input, thereby improving the control performance of the SEA.