High-rise building made of CLT increases significantly its own weight. Therefore, the collapse of the wall bottom is concerned. Main purpose of this study is to verify the effect of the reinforcement with screws for avoiding the collapse of the CLT wall bottom by extreme vertical load. Test pieces of CLT wall bottom were reinforced by screws. As a result, we got better structural result with screw reinforcement than without screw. From these experimental results, the reinforcement of CLT wall bottom using screw at perpendicular angle to the fiber direction is effective in workability because it does not need seat-dig hole.