A liquid collection bag (7) is used as a part of an extracorporeal circuit (1) and is connected via a tube (10) to a storage container (6) containing a priming solution. The collection container (7) collects the priming solution from the storage container (6) by a pressure differential between the pressure inside the collection container and the pressure inside the storage container. The liquid collection container (7) is a flexible bag body having a partition (74) part dividing the inside of the bag body into a first space (711) and a second space (712). In addition, a communication part (73) communicates the first space with the second space.
