Backdrivability is highly required in various robotic fields such as industrial, welfare, and wearable robots. To miniaturize the system, gear reducers are often used. In gear reducers, there are backlashes, which deteriorate control performance. However, only from the view point of backdrivability, backlash has an ideal characteristic because the load side idles within the backlash width (i.e. When someone put external force at the load side, the load side does not hit the motor side within the backlash width). This means that external forces from the load side only feel the load-side impedance without motor-side impedance. The proposed method uses this idling characteristic to enhance backdrivability. Moreover, in industry, there is a trend toward the expansion of the use of load-side encoders thanks to their cost reduction. Based on this industrial trend, the proposed method is realized using both the motor-side and load-side encoder information to improve backdrivability. Simulation and experimental results demonstrate proposed method's effectiveness.