A haptic master with a 3-axis gimbal structure has been developed to control active-steering catheter robots. The operator's forearm may collide with a link of the master device during the operations. This paper reports a method to avoid the collision. Distance sensors are attached to the expected collision points, and artificial potential fields are defined around the sensors. The closest link to the ground is controlled as if the potential fields apply a repulsive force. Other links except the avoidance-controlled link are also controlled simultaneously to maintain the orientation of the master handle. This scheme is experimentally verified.