This paper is about the design of a new gravity compensator for the exo-skeleton device. The exo-skeleton device is developed for increasing the torque of the human body joint for the purpose of helping the disabled or military soldiers. So far, most exo-skeleton device has been actuated by the motors, but motors are limited in energy such that a short durability is always a big problem. In this paper, a new exo-skeleton device applying the gravity compensator is proposed to reduce the torque load applied to human body joint. The applied gravity compensator is designed using a tortional bar spring, and its structure and characteristics are studied. The performance of the gravity compensator is studied through a kinematics simulation. Also the design of the exo-skeleton device is presented.