The aim of this study is to evaluate the bubble generation behavior for the practical use of the air leak measurement system for pneumothorax patients. The method for measuring the air leak flow rate has already been developed, using the bubble volume and bubble generation frequency in the chest drainage unit. One of the problems for the practical use of this method is that the flow rate is calculated with the bubble volume as a constant value. However, it is known that the bubble volume changes depending on the amount of drainage accumulated in the chest drainage unit and the flow rate flowing into the unit. Therefore, we investigated the correlation between the pressure wave and the bubble volume for the development of air leak measurement system that can compatible with changes of bubble volume. We discovered that there is a correlation between the pressure difference when a bubble separates and the bubble volume. We succeeded in measuring air leaks with high accuracy using the bubble volume estimated from the pressure wave.