This paper describes the mechanism and real training with the three degrees of freedom (3-DOF) mouth opening and closing training robot WY-2 (Waseda Yamanashi-2) that is developed to train the patients who have problems on their jaw movement. WY-2 consists of a mechanical, actuation, sensor, and control systems. The seesaw mechanism inserted in the patient's mouth opens the mouth by squeezing the master manipulator that is controlled by the doctor. The force sensor measures the patient's biting force. A personal computer integrates and controls the other systems. As a result of therapy with this robot for the real patient, the mouth opening distance increased.