PROBLEM TO BE SOLVED: To provide a stock solution treatment apparatus and a method for operating the stock solution treatment apparatus, which can perform a leak check easily, can easily perform an air bleeding work, and can effectively clean a flow path. SOLUTION: A filter 10 having a filter member that does not allow gas to permeate a stock solution such as pleural and ascitic fluid or plasma, and the filtrate filtered by the filter 10 are supplied to concentrate the filtrate to form a concentrated solution. A method for operating a stock solution treatment apparatus 1 comprising a concentrator 20, wherein a filter 10 comprises a main body 11 having a flow path to which the stock solution is supplied and an internal space separated by a filtering member, and a main body. The internal space of the portion 11 is provided with a port that communicates with the outside, and pressurized gas is supplied from the port to the internal space in a state where the internal space of the main body portion 11 is airtightly isolated from the outside. Measure the gas pressure. [Selection diagram] Figure 1【課題】リークチェックを簡便に行うことができ空気抜き作業も容易であり流路の洗浄を効果的に行うことができる原液処理装置および原液処理装置の操作方法を提供する。【解決手段】胸腹水や血漿などの原液を濾過する気体を透過しない濾過部材を有する濾過器１０と、濾過器１０よって濾過された濾過液が供給され濾過液を濃縮して濃縮液を形成する濃縮器２０と、を備えた、原液処理装置１の操作方法であって、濾過器１０が、原液が供給される流路と濾過部材によって隔離されている内部空間を有する本体部１１と、本体部１１の内部空間と外部とを連通するポートと、を備えており、本体部１１の内部空間を外部から気密に隔離した状態で内部空間にポートから加圧気体を供給して内部空間内の気体の圧力を測定する。【選択図】図１
