A biological component treatment cassette (blood component collection cassette (28)) is configured to be attachable to a separation device (centrifugal separation device (14)), and a flow path (42) is formed in an interior portion thereof. The biological component treatment cassette includes a wall portion forming a part of the flow path (42, and is equipped with pump action members (first and second pump action members (58, 66)) formed of a soft material and which are pressed by pumps of the separation device. The pump action members include pump pressed portions (first pump pressed portions (58a), second pump pressed portions (66a)).
