The 2D/3D hybrid tsunami numerical model is developed in which the conventional 2D model is adopted for the calculation in the wide region located far from the coastal structures although the 3D non-hydrostatic pressure numerical model is used in the limited region adjacent to the structures. Applicability of the domain connection technique is examined by comparing the numerical results obtained by the present hybrid model with those obtained by applying the 3D non-hydrostatic pressure numerical model for the whole domain. Further, the results of the model tests are compared with the numerical results obtained by both the present hybrid model and the 2D model, to examine the validity of the present model. It is shown that the present model reduces a calculation load significantly comparing to the case adopting the 3D model for the whole domain and reproduces the characteristics of three-dimensional complicated flow around the opening of breakwater which cannot be reproduced by the 2D model.