Radiofrequency Ablation (RFA) is a low invasive treatment to eliminate liver cancer cell. However, it is difficult to place a needle accurately especially after the first insertion because the ultrasound image is distorted by micro bubbles generated in the first cauterization. To solve this problem, we developed the navigation system which consists of 3D tracking sensor, ultrasound imaging system, user-interface software and a simple 2DOF navigation robot to support the second or third insertion task. In this paper, newly user-interface and the simple robot are presented. The robot holds the needle guide with two arms, which have a pivot joint on each tip to determine the orientation of the needle. Each arm is separable for the sterilization. System accuracy in in-vitro testing was 6.17 ± 0.59mm, and the main error was considered to be the ultrasound image calibration and the rigidity of the needle, that should be solved for future tasks. With the navigation information and the robot, surgeon can operate the RFA needle more precisely.