A new type of wave dissipating caisson has been developed and is called as a curved slit caisson in the present paper. The permeable front wall is an arc-shaped slit wall and the shape of wave chamber is a quarter circle in the side view.
　A series of model experiments has been conducted to investigate the following aspects of the curveed slit caiison:
(1) wave reflection, overtopping, and transmission due to random waves,
(2) wave forces on structural members of the caisson,
(3) resultant wave forces on the caisson and the stability against sliding.
　it is concluded that the wave reflection of curved sit caisson is less than that of ordinary type of wave dissipating caisson and is equivalent to the wave reflection of caisson covered with wave dissipating concrete blocks.
　As to wave forces, shock pressures are caused at the moment when the water surface in the wave chamber impacts upwardly the top of curved slit wall. These shock pressures must be considered in the structural design of members bounding the wave chamber. The resultant wave forces effective to sliding and over-turning of the caisson, howevere, is not large, since downward wave forces act on the bottom slab of the wave chamber. It is confirmed that the sliding distance of curved slit caisson is considerably less than that of ordinary caisson breakwaters.