This report is to do with the experimental results of the performance of the wall ventilator conducted by the present author. As the results of these experiments, the ventilation mechanism of the wall ventilator was made clearer, and it became evident, moreover, that to increase the ventilation efficiency, special attention should be given to the following three points : 1) As the ventilation action depends largely upon the aft pipe, it is highly desirable to design the aft pipe as large as possible. 2) Moreover, the ventilation efficiency has much to do with the shape of the passage from the main pipe to the aft pipe, and accordingly, it is important to make it hydrodynamically smooth. 3) It is highly desirable to make the diameter ratio of the fore pipe entrance to the aft pip moderate. In case when the ratio is excessively large, the fore pipe often disturbes the ventilation action due to the aft pipe only.