There have been a lot of researches about developing the lower limb exoskeleton not only for elderly anddisabled people but also ordinary people. The users could feel uncomfortable when wearing the robot becauserotation axes of the lower limb joints are different with that of the robot and the robot is too heavy to disturb the natural lower limb movements. However, the evaluation index of the uncomfortableness has not been completely established yet. In this paper, we decided surface electromyography (sEMG) level as the index of uncomfortableness because the activation level of human muscle is different when the load is added during walking. We compared sEMG of vastus medialis (VM), hamstring (HAM), tibialis anterior (TA) and gastrocnemius (GAS) during normal walking and stair walking whether the user wearing the system or not.