PURPOSE: To eliminate mixing of air in a bag for separating blood constituents and to obtain hematic preparations from the whole blood at high yield even using a leukocyte removal filter by discharging to that filter the air contained in the bag for storing the blood with leukocyte removed.

CONSTITUTION: Blood collected with a needle 1 is stored through a blood collecting tube 2 in a bag 3 containing an anticoagulant and placed in a storage temporarily. The blood in the bag 3, with the leukocyte removed through a leukocyte removal filter 5, is stored in a bag 6. The air remaining in the bag 6 with the blood from which leukocyte has been removed is discharged to the leukocyte removal filter 5 by closing a blood transporting tube 4' and opening a blood transporting tube 11. Then, with the tube 11 closed and with the tube 4' opened, the blood remaining in the downstream of the removal filter 5 is stored in the bag 6. Thus, hematic preparations are efficiently obtained from the whole blood.