<p>A remote-controlled robot for CT-guided needle insertion has been developed to prevent a doctor from radiation exposure. However, it is difficult for a doctor to recognize abnormal states of insertion when the doctor uses the robot because the doctor cannot obtain force sense information from the needle directly. Such an abnormal state occurs when a needle contacts with a bone. Therefore, we propose detecting abnormal states of insertion if force sensor value exceed a threshold and stopping the robot automatically. First, we conducted experiments to determine thresholds. We measured force values when a doctor feels the sign of plastic deformation in needles. In consideration of the stop time delay, thresholds were set by subtracting the rise values of force from the measured force values. Then, we verified that the robot can stop appropriately by the thresholds without occurring plastic deformation.</p>