The author has tried to clarify the differences between two formulae, Lagally's and so-called linearized, and found that its cause lies in an approximate treatment of the boundary condition, but this is corrected in counting for the variation of the displacement volume. In this stand point, however, we have to count the second approximation for the boundary condition. Fortunately, the wave resistance formula does not differ with two formulae, but for the trim and sinkage their difference is very serious one. He explains theoretically and numerically these difference with experimental data which can be usefull. In the mean time, he sugguests a simple formula which gives roughly a wave resistance from the recorded wave profile in a fairly wide range of ship speed.