A clamp for a blood bag system includes a protrusion section which presses a tube, a locking section having a first engagement section and a second engagement section that form therebetween an engagement groove in which the protrusion section is positioned and by which engagement can be made, a first engagement release section which releases an engaged state between the first engagement section and the protrusion section； and a second engagement release section which releases an engaged state between the second engagement section and the protrusion section.
