To provide a blood component sampling circuit for filtering out a predetermined cell in a predetermined blood component with high precision without elongating a working time.

The blood component sampling circuit 1 is provided with a leucocyte filter unit 40 which is formed by integrating a reserver 42 capable of storing platelet-rich plasma centrifugally separated by a centrifugal separator 20 by a single sampling cycle; with a leucocyte filter 41 filtering out the leucocyte. The platelet-rich plasma separated by the centrifugal separator 20 is temporarily stored in the reserver 42 for each sampling cycle and the platelet-rich plasma is guided to the leucocyte filter 41 to filter out the leucocyte.