This paper introduces an implementation technique of sensor-less control on two joint robot manipulator. A great number of robots have been developed and most of them mount many kinds of sensors. However, use of the many sensors increase cost of robots and decrease reliance. Shimada et.al. have presented a unique sensorless control technique for electric motor driven mechanical systems. The feature of the technique is to mount mechanical springs on joints of robots. Furthermore, they have tried to extend the sensorless control technique to robots with revolutional joints. However, the performance of the presented observer was not enough to practical use. To fix the problem, we have tried to design time varying observer considering the time varying characteristics on the mounted mechanical springs. This paper introduces the simulation and experimental results of the presented control technique.