Safety is one of the most important issues in rehabilitation robot suits. We present a new rehabilitation robot suit equipped with two mechanical safety devices. The robot suit assists a patient's knee joint. The safety devices consist of only mechanical components without actuators, controllers, or batteries. We expect that the safety devices guarantee the safety even if the computer does not work. In this paper, we firstly describe the rehabilitation robot suit with the two safety devices. Secondly, we show the basic structure of the robot suit. Finally, we explain the experiment device which we built in order to examine the usefulness of the two safety devices.