In a blood-flow-path switching device and a blood-bag system, a tube-shaped body (68) includes a body tube (69) extending in an axial direction and a branching tube (71) extending in a direction branching from the axial direction, and a blocking part (74) is provided in a hollow section (69c) of the body tube (69). A communicating part (70) movable in the axial direction is provided in the hollow section (69c). By moving the communicating part (70) in a pushing direction and creating an opening by penetrating the blocking part (74), a communication of a first port (86) and a third port (90) is blocked, and at the same time, the first port (86) and a second port (88) are communicated with each other.
