Abstract—In this paper, a control system of the sensory feedback device for myoelectric prosthetic hand users, which was developed in our previous study, was improved to express the hardness of an object continuously. The sensory feedback device is worn on user’s upper arm. When the finger of the myoelectric prosthetic hand grabs the object, a contact force on the object is detected by a pressure-sensitive sensor attached on a finger cushion of the myoelectric prosthetic hand. Moreover, the hardness of the object is calculated. According to the hardness of the object, a reference input to realize the corresponding winding speed of the belt is generated by a reference input generator. Then, the motor of the feedback device is controlled to track the reference input by using the self-tuning Proportional- Integral-Derivative (PID) control technique, taking parameter variation into account. Thus, the belt of the feedback device is wound by the motor and tightens the user’s upper arm, so that the user can feel a tactile sense. Finally, confirmation tests are conducted to verify the effectiveness of the improved control system. As a result, the hard object and the soft object are able to be distinguished with an average accuracy of 92.5%.