To provide a blood cell separator for collecting blood components containing a less amount of unnecessary components and a method for separating and transferring blood components.

A bag joined body (the blood cell separator) 1 comprises five bags, a blood collecting bag 10, a blood platelet preservation bag 20, a red blood cell preservation bag 30, a preservation solution retaining bag 40, and a blood plasma preservation bag 50, joined by prescribed tubes respectively. The blood collecting bag 10 is connected with the blood platelet preservation bag 20 by a first tube, is connected with the red blood cell preservation bag 30 by a second tube branching from the first tube, and is connected with the retaining bag 40 by a third tube branching from the first tube. A white blood cell removal filter 60 is provided on the side of the blood collecting bag 10 of the branching part of the second tube in the middle of the first tube. A filter 70 for removing white blood cells and blood platelets is provided in the middle of the second tube.