Safety is one of the most important issues in rehabilitation robot suits. We have proposed the structure of a rehabilitation robot suit equipped with two mechanical safety devices. The robot suit assists a patient's knee joint and the safety devices consist of only passive mechanical components without actuators, controllers, or batteries. We call one device the 'velocity-based safety device' and the other the 'torque-based safety device'. We expect a robot suit with the safety devices to be able to guarantee the safety even when the computer fails to operate functionally. In this paper, we begin by reviewing the characteristics of the safety devices and the structure of the rehabilitation robot suit equipped with the safety devices. Then we show a prototype robot suit developed based on the proposed structure. Finally, experimental results are demonstrated to verify the effectiveness of the safety devices in the prototype robot suit.