Characteristics of pneumatic-type wave power extractors are examined on the basis of both the results of the approximation theory and the two dimensional experiments in this paper. The extractors consist of a front air chamber and a front curtain-wall.
　A closed form theory based on thermodynamics is derived to predict the efficiency of the extractor from the informtaion of incident waves and the dimensions of air chamber. The calculations support the result of experiments well in the conditions that the relative water depth h/L<0.25, the nozzle area ratio ε<1/50 and the relative depth of the curtain-wall dc/Hi>0.67, where ε is the ratio of the nozzle area to the area of the chamber,dc is the depth of the lower end of the cur tain-wall.
　The optimum nozzle area ratio ε increases from 1/300 to 1/125 with increasing wave height and with decreasing wave period. The width of air chamber B when the
efficiency becomes maximum is from 0.8 to 1.5 times the water depth. The depth of the lower end of curtain-wall at the maximum efficiency is 0.5～1.0 times the in
cident wave height.
　It is also clarified that the efficiency of the scale model unit is higher than that of the prototype because the efficiency is controlled by the parameters of atmospheric pressure and temperature as well as by other parameters.