To evaluate motions and joint reaction forces of the total knee prosthesis during deep knee flexion such as kneeling and sitting straight, a simulator that reproduces the passive motion of the knee has been developed. The main feature of the simulator is that the knee joint is accurately and repeatedly moved from 0° to 180° flexion angle in six degrees of freedom. Moreover, the tibiofemoral and patellofemoral motion and joint reaction forces can be continuously measured. Assuming that muscular force is mainly generated with a quadriceps femoris muscle, the similar force vector is produced by two motors. The custom-designed posterior stabilized type total knee prosthesis which can be flexed to 180° has been inserted in the bone model and evaluated. As a result, it was confirmed that this simulator was able to measure the motion and joint reaction force of the knee with high repetition accuracy. The experimental results showed the same tendency with those in the previously performed cadaveric experiment. Hereafter, cadaver knee can be used for the evaluation of the knee prosthesis using the proposed simulator with high accuracy.