In this paper, authors report about the loads on ship caused by horizontally laid cylindrical heavy cargoes at rolling of ship. In such a case, a coil called “key coil” is usually used to prevent the motion of coils. The key coil is a coil which is laid in a narrower space than its diameter and held on a high position. Authors developed the calculating method for cases with and without a key coil, and their numerical results were compared with the experimental values. Results of this investigation can be summarised as follows : (1) Loads on a side wall and a bottom can be obtained theoretically with a considerable accuracy. (2) The key coil should be put apart from a side wall. (3) If a coil which lies apart more than two coils from a side wall is used as a key coil, the design load F on a side wall can be given by a following expression, F =2.5 W sinθ where, W is a weight of a coil and θ is an angle of inclination.