Wave analysis is proposed for deriving amplitude function of elementary waves composing nonstantionary wave pattern generated by a ship which is forced to oscillate and is running on a calm water with forward velocity. The purpose of this wave analysis is especially to verify the validity of theory of resistance increase in waves in predicting the structure of nonstationary wave pattern due to an oscillating ship. Wave analysis method proposed here is similar to that which is used in research on stationary wave making resistance theory and is called Newman-Sharma method. Wave patterns generated by an oscillating ship, however, vary with time in contrast with those in stationary wave making and accordingly a process is devised for eliminating time factor and for deriving wave amplitude and phase distribution in space available for analysis. With this process we can easily extract space distribution information of amplitude and phase of nonstationary waves from wave height data which are obtained with repeating measurements a few times at only a point in model basin. From the results of wave analysis of measured wave pattern compared with theory we can conclude that slender body theory can predict wave amplitude function distribution fairly good. And a little interaction effects between stationary and nonstationary waves are observed.