A 66-year-old male with spontaneous pneumothorax underwent chest tube drainage in other hospital. After tube drainage, chest X-ray showed that the lung fully expanded and an air leakage was not visible. However, clamping the chest tube led to the collapse of the lung, and he transferred to our hospital. A continuous suction unit with pressure and bubbling time history monitoring system was used to detect intermittent air leakages( MS-009T). He underwent video-assisted thoracoscopic surgery. An air leakage from the right lung successfully closed. A new continuous suction unit was useful in detecting an air leakage which could not be confirmed by visual inspection.