PURPOSE: To ensure adequate injection of an anticlotting agent in a specified amt. with respect to the amt. of the blood to be taken even if a blood pump is not used.

CONSTITUTION: This plasma taking method comprises injecting the necessary anticlotting agent at the specified ratio by an anticlotting agent injecting pump into the blood at the time of taking the blood by feeding back the increased amt. of the blood successively accumulated into a reservoir at the time of the taking to the pump at the time of taking a set amt. of the blood under the reduced pressure of the reservoir and once storing this blood in the reservoir, then returning the blood under the reduced pressure of the reservoir while taking the plasma from the blood in to the reservoir.