Model tests of two container ships in oblique regular and irregular waves were carried out at the seakeeping tank of S. R. I., and the relative wave elevations at various positions of the models' hull were measured by means of capacitance wave probes attached on the hull. The relative wave elevation induced by combined ship motions as pitch, heave and roll and the wave elevation can be calculated by the strip method. The deformation of the wave surface near the hull which is induced by hydrodynamic interaction between ship's body and wave is estimated by the Tasai's two dimensional theory, and it is added to the above-mentioned relative wave elevation. The comparison of the test results with the computed values shows that : a) calculations including the hydrodynamic interactions show good agreement with the experiment, generally speaking, in head and bow seas, b) the measured values in beam sea lie between calculated values including and excluding hydrodynamic interactions, c) disagreement between measured and calculated values is most remarkable in quartering sea, except one for the stem provided that the estimation is made excluding hydrodynamic interactions, d) the amplitude distributions of the relative wave elevations measured in irregular waves show good agreement with the estimated one by the linear superposition of the response amplitude operator and sea spectrum.