The object of the invention is to provide a blood separation device that can reduce the total time for drawing blood to obtain high-concentration platelet liquid, thereby reducing the binding time of the blood donor. The device includes a temporary storage bag (Y2) (also serves as a buffy coat bag) which is a whole blood bag for storing whole blood drawn from a blood donor. The controlling unit of the device controls the device to draw whole blood from the blood donor in parallel with at least either a circulation flow step or an acceleration step, thereby storing the drawn whole blood in the temporary storage bag (Y2).
