The clear understanding of the generation mechanism of the impulsive pressure by breaking wave is indispensable for the design of a vertical-wall caisson which may receive the pressure acting on a vertical wall. Based on experimental results the generation mechanism of teh impulsive presure was investigated, and a simple
model which describes the relation between the wave front and the impulsive pressure was made.
　In the model three regions are considered acoording to the angle, β, between the wave front and the wall. In the first region the Wagner type pressure can be observed and in the second region the Bagnold type pressure acts on the wall. The third region is the transition region of the two. Using the model with the values of the mass coefficient, km, the effective height coefficient, kl, and the minimum air thickness coefficient, kao, the pressure tims history can be calculated.