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