In ship structure design, estimations of wave loads and structural response to them should be made in relation to sea condition. Since the estimation of wave loads is usually carried out component-wise, accuracy of estimated response must be examined by checking not only magnitudes of responses to component wave loads but also phase differences between them. From this point of view, in this paper, confirmation was made first on the accuracy of wave load estimation calculation by comparing with results of model experiment, focussing on phase differences between wave load components. Then, DISCRETE ANALYSIS METHOD based on full ship 3-D FEM was developed, and its reliability was confirmed. Next, trial calculations of structural response to superposed wave load components, were made on a 63, 000 DWT bulk carrier. From this calculations, the following results are obtained: (1) Stress components on double bottom induced by inner and outer pressure mostly cancel each other. (2) Resultant stress on double bottom due to combination of hull girder bending and local bending is lower than the stress value obtained by simple summation of stress components, owing to the effect of phase difference.