In this study, an optimization method of feedback control inputs for a posture control of a six-legged robot was developed. The authors had proposed a method to control using an optimum servo system as a posture control method of a six-legged robot. As a problem of this method, because the feedback (FB) gain was switched at the time of switching the swing leg, the control inputs becomes discontinuous and there was a problem that the posture variation increases. After that, FB inputs of the thigh link obtained by optimum servo system were optimized. Then, we design a control system that suppressed the posture variation that occurs during swing leg switching. The effectiveness of the proposed control method was confirmed using a 3D model of a six-legged robot.