A blood reservoir tank (20) for retaining blood comprises a first reservoir section (21), a second reservoir section (22), and a third reservoir section (23) that is provided between the first reservoir section (21) and the second reservoir section (22) and by which the first reservoir section (21) and the second reservoir section (22) communicate. A first blocking member (31) and a second blocking member (32) are provided in the blood reservoir tank (20). The first blocking member (31) is configured so as to be able to block communication between the first reservoir section (21) and the third reservoir section (23). The second blocking member (32) is configured so as to be able to block communication between the second reservoir section (22) and the third reservoir section (23).