Abstract: An example of the closed-type blood reservoir of the invention is furnished with an outer shell in which a space is formed within its interior, a flexible septum that is interposed between a blood storage chamber shell and a volume adjustment chamber shell and that divides the space into a blood storage chamber for storing blood and a volume adjustment chamber for storing volume adjustment liquid, a blood inlet port, a blood outlet port, and a blood storage chamber air discharge port that are provided in the blood storage chamber shell such that they are in communication with the blood storage chamber, and a volume adjustment liquid port that is provided in the volume adjustment chamber shell such that it is in communication with the volume adjustment chamber, for injecting and ejecting the volume adjustment liquid into and away from the volume adjustment chamber, wherein the blood inlet port and the blood outlet port each are provided tangentially to the inner surface of the blood storage chamber shell such