A novel control method for the walking assistance device using predefined walking trajectory used to walk for the elderly or the patients with weak leg muscle on stairs from plain more safely and naturally is proposed in this paper. Two control method, torque control and impedance control, used per their usage purpose are introduced, and the later one is focused in this paper. To make sure the use of safety, two situations, putting swing leg in front of stair too close or too far, while a user wearing assistance climbing up on the stairs through even ground is considered. If the user faces these situations walking with the apparatus using impedance control, falling or collision between apparatus and stair are happened more easily than level walking because of lots of environment facts need to be considered like the distance between user and stairs. One of the most important environment facts is recognizing of the stairs, therefore, to prevent the user from the danger in each situation, ultrasonic sensor is used as a safety system to keep space, and we called safety distance, between foot part of walking device and stair. The value of safety distance is not only defined as a switch to change the walking trajectory between the plain mode and the stair mode but also used to decide the ideal stride of trajectory while walking to stairs from even ground. Finally, the result of walking experiment shows that the safety walking experience by wearing our walking assistance device can be achieved.