Due to urbanization, it is difficult to secure a large knuckle crane workspace. To solve this problem, we developed a small knuckle crane combined with a one-ton truck. In this study, the safety of small knuckle cranes is evaluated through Finite Element Analysis. Shape optimization was performed using the Design of Experiment for parts speculated to have failed from fatigue. As a result, maximum equivalent stress of a plate in link speculated to have failed from fatigue was reduced by approximately 84.2%.