Fluid–structure interaction (FSI) problems are important because they may induce serious damage to structures. In some FSI problems, the interaction mechanism is strongly dependent on the wave propagation across the solid–fluid interface. In this study, we attempted a quantitative evaluation of the effect of the solid surface wettability on the wave propagation across the solid–fluid interface with FSI in the case of longitudinal wave propagation vertically toward the interface. During the experiments, while the water was continuously compressed by the solid buffer motion, cavitation bubbles appeared being originated from the buffer–water interface as a result of the transmitted tensile wave propagating across the interface in a cycle. It was confirmed that interfacial boundary condition as wettability could change the wave transmission behavior owing to changes in the cavitation occurrence. It was also confirmed that the worse the wettability, the more severe the cavitation intensity, and the greater the difference between the energy lost by the buffer and the energy stored in the water. Consequently, the effect of the cavitation inception on the wave propagation at the solid–fluid interface with FSI could be quantitatively evaluated by considering the energy transferred from the solid to the water.