To provide a device to separate stem cells and precursor cells from umbilical cord blood in which mingling of bacteria is eliminated, and in which loss of large quantity of cells by separating operation can be prevented.

A device comprises a parent bag 3 containing umbilical cord blood to be separated to blood components by centrifugal separation, a first child bag 5 to which blood plasma in the parent bag 3 is moved to be contained, a means to separate the blood plasma in the first child bag 5 to a blood plasma component and a leucocyte component, a second child bag 9 to which the blood plasma component at an upper layer of the first child bag 5 is moved to be contained, a freezing bag 11 to which the leucocyte component, in the first child bag 5 is moved to be frozen and stored, and tubes making these bags communicate with each other for moving the separated blood components, where stem cells and precursor cells are separated from the umbilical cord blood.