A biological component treatment cassette (blood component collection cassette (28)) is configured to be attachable to a separation device (centrifugal separation device (14)) adapted to separate a biological component from a liquid containing at least one biological component, and a flow path (42) is formed in an interior portion thereof. The biological component treatment cassette includes a sheet-shaped cassette main body (40), and a first pump action tube (58), both ends of which are connected to the flow path (42) of the cassette main body (40), together with a portion thereof protruding from an outer peripheral edge portion of the cassette main body (40), and which is made from a soft material that is pressed by a pump (80) of a separation device.
