A blood bag system includes a BC pooling bag for centrifugation of a buffy coat, a 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, a first tube connecting the BC pooling bag and an inlet of the filter, a second tube connecting the platelet preserving bag and an outlet of the filter, and a cassette to be fixed in the centrifugation and separation apparatus. The first tube and the second tube are disposed within the cassette. The cassette includes a first clamp section for closing and opening the first tube, and a second clamp section for closing and opening the second tube.