This paper introduces a sensorless grasping and movement control technique on robot hands. A great number of robot hands have been developed and most of the hands mount many kind of sensors. However, use of the many sensors increase the cost of robot hands and decrease the reliance. Meanwhile, Shimada et.al. presented an unique sensorless control technique for electric motor driven mechanical systems. Furthermore, they have tried to extend the sensorless control technique to multi-finger robot hands. The observer is fragile for coulomb friction. To solve this problem, we introduce a nonlinear observer. This paper describes a design way of the observer and show some simulation results.