In a blood bag system mounted in a centrifugation and separation apparatus, a filter is settable in different appropriate orientations at storage time and usage time, and first and second tubes and a filter are arranged respectively in appropriate orientations during use. The blood bag system includes a BC pooling bag for centrifugation of buffy coat, the filter for removing white blood cells from a supernatant liquid transferred from the BC pooling bag, a platelet preserving bag for reserving the supernatant liquid that has passed through the filter, the first tube connecting the BC pooling bag and an inlet of the filter, the second tube connecting the platelet preserving bag and an outlet of the filter, a cassette fixable in the centrifugation and separation apparatus, an attachment for holding the filter, and a hinge section tiltable relative to the cassette with reference to an axis in the circumferential direction.
