PROBLEM TO BE SOLVED: To provide a washing treatment bag capable of washing a cell suspension with a simple operation. A cleaning bag 10 includes a storage chamber 20 formed by stacking a pair of resin films 44 and 46 and sealing a peripheral edge portion 22 thereof, and a port 24 communicating with the storage chamber 20. The storage chamber 20 includes a first storage chamber 12 configured to be able to store the cell suspension 80, and a second storage chamber 14 containing a replacement solution 86 for diluting the cell enrichment section 82 in which cells are concentrated. It has a weak seal portion 16 that separates the first storage chamber 12 and the second storage chamber 14 and can be opened by pressure. [Selection diagram] Fig. 2【課題】簡便な操作で細胞懸濁液の洗浄を行うことができる洗浄処理用バッグを提供する。【解決手段】洗浄処理用バッグ１０は、一対の樹脂フィルム４４、４６を重ね合わせてその周縁部２２を封止して形成された収容室２０と、収容室２０に連通するポート２４とを備え、収容室２０は、細胞懸濁液８０を収容可能に構成された第１収容室１２と、細胞が濃縮された細胞濃縮部８２を希釈する置換液８６を収容した第２収容室１４と、第１収容室１２と第２収容室１４とを隔てるとともに、圧力により開通可能な弱シール部１６とを、有する。【選択図】図２
