In the industrial motor drive system which is composed of a motor and load connected with a flexible shaft, a torsional vibration is often generated because of the elastic elements in torque transmission. This vibration, which is generated in a two-mass mechanical system. To solve this problem, recently there has been a lot of researches for the robust control relevant to the $H_{infty}$ control suppressing the torsional vibration and rejecting the torque disturbance. In the case of the $H_{infty}$controller, however, the command tracking property becomes worse because of overshoot during transient response. For this reason the $H_{infty}$ controller, which includes the two-degrees-of-freedom(TDOF) controller, is designed in order to improve command tracking property. However, it also includes complexity realizing this controller. In this paper, a new $H_{infty}$ controller with partial state feedback is proposed. Proposed $H_{infty}$controller has simple structure but satisfies with the fast command tracking property and the attenuation of disturbances and vibrations simultaneously, just like the complicated TDOF $H_{infty}$ controller.