This paper proposes a novel motion planning method in rough terrain that improves our previous work. The previous method can generate a collision-free path within a short time, however, there is room to improve the quality of its path, especially about the length of its path. In this work, we add a path deformation step after a path generation step. The path deformation is performed by optimization. The objective function of optimization consists of path length, difference between original path and deformed path, and risk of deformed path. Experimental results show that the proposed method can deform a re-planned path appropriately and can reduce the length of the path.