In this study, fluid resonance in the narrow joint gaps of a caisson-type seawall is investigated experimentally and theoretically. In particular, focus is placed on the effect of incident wave angle for the occurrence condition of the fluid resonance and the amplification of wave height in the gaps at resonance. 3-D wave basin with a snake-type wave generator is used in the experiments, and the theoretical analysis is carried out using the method of matched asymptotic expansions. Consequently, it is found that the incident wave period and the amplification on wave height in the gaps as fluid resonance occurred are independent of incident wave angle and can be predicted using the knowledge subject to the case that the incident wave progress perpendicular to the seawall.