In the management of chest drain after thoracic surgery, it is important to egest fluid and air which accumulate in the pleural cavity and to gain information such as air leakage, bleeding or pus discharge. To achieve these purpose, continuous chest drainage system is necessary for thoracic surgery. In addition, we have to understand the particularity in the pleural cavity and the structure of continuous chest drainage system. Traditional drainage system is based on 3-bottle system. Recently, we can use new drainage system, such as Thopaz, which is called digital drainage system. There are several studies comparing digital drainage system with traditional drainage system, but the superiority of digital drainage system to traditional drainage system is not confirmed.