For the ocean development, work vessels are important. The operability of such vessels are heavily affected by sea conditions. Here, for increasing the operability of floating cranes, we tried to suppress the swinging motion of a load in waves. For that purpose, we developed a control system of the swing of a load, through controlling body motions of a floating crane, and also developed a numerical simulation method for this estimation. Furthermore, we adopted the so called pneumatic control system for controlling the motion of a floating crane.