A blood bag system comprising: a first bag for containing blood; a second bag for containing a blood component obtained by centrifuging the blood in the first bag; a third bag for containing an additive solution; characterized by one clamp capable of closing respective flow channels (36a, 38a) of a second tube and a third tube, wherein a first tube connected to the first bag is connected to the second tube connected to the second bag and the third tube connected to the third bag via a branching section, the one clamp includes a plate-shaped base (92; 154), the base (92; 154) is provided with: a first insertion hole through which the second tube is inserted; a second insertion hole through which the third tube is inserted; a first slit (104; 104a; 104b; 104c; 104d; 104e; 150; 160) which extends from the first insertion hole and which is configured to press an outer circumferential surface of the second tube inward so as to close the flow channel of the second tube; and a second slit (106; 152; 160) which extends from the second insertion hole and which is configured to press an outer circumferential surface of the third tube inward so as to close the flow channel of the third tube, the second tube and the third tube are inserted through the base, the base includes the first slit (104; 104a; 104b; 104c; 104d; 104e; 150; 160) and the second slit (106; 152; 160), the base has a first side and a second side located on sides opposite to each other, the first insertion hole and the second insertion hole are arrayed along a direction from the first side toward the second side, the first slit (104; 104a; 104b; 104c; 104d; 104e; 150; 160) and the second slit (106; 152; 160) extend respectively from the first insertion hole and the second insertion hole toward the first side, and an operation section operable by a finger of a user is provided on the second side. a first bag for containing blood; a second bag for containing a blood component obtained by centrifuging the blood in the first bag; a third bag for containing an additive solution; characterized by one clamp capable of closing respective flow channels (36a, 38a) of a second tube and a third tube, wherein a first tube connected to the first bag is connected to the second tube connected to the second bag and the third tube connected to the third bag via a branching section, the one clamp includes a plate-shaped base (92; 154), the base (92; 154) is provided with: a first insertion hole through which the second tube is inserted; a second insertion hole through which the third tube is inserted; a first slit (104; 104a; 104b; 104c; 104d; 104e; 150; 160) which extends from the first insertion hole and which is configured to press an outer circumferential surface of the second tube inward so as to close the flow channel of the second tube; and a second slit (106; 152; 160) which extends from the second insertion hole and which is configured to press an outer circumferential surface of the third tube inward so as to close the flow channel of the third tube, the second tube and the third tube are inserted through the base, the base includes the first slit (104; 104a; 104b; 104c; 104d; 104e; 150; 160) and the second slit (106; 152; 160), the base has a first side and a second side located on sides opposite to each other, the first insertion hole and the second insertion hole are arrayed along a direction from the first side toward the second side, the first slit (104; 104a; 104b; 104c; 104d; 104e; 150; 160) and the second slit (106; 152; 160) extend respectively from the first insertion hole and the second insertion hole toward the first side, and an operation section operable by a finger of a user is provided on the second side. a first insertion hole through which the second tube is inserted; a second insertion hole through which the third tube is inserted; a first slit (104; 104a; 104b; 104c; 104d; 104e; 150; 160) which extends from the first insertion hole and which is configured to press an outer circumferential surface of the second tube inward so as to close the flow channel of the second tube; and a second slit (106; 152; 160) which extends from the second insertion hole and which is configured to press an outer circumferential surface of the third tube inward so as to close the flow channel of the third tube, the second tube and the third tube are inserted through the base, the base includes the first slit (104; 104a; 104b; 104c; 104d; 104e; 150; 160) and the second slit (106; 152; 160), the base has a first side and a second side located on sides opposite to each other, the first insertion hole and the second insertion hole are arrayed along a direction from the first side toward the second side, the first slit (104; 104a; 104b; 104c; 104d; 104e; 150; 160) and the second slit (106; 152; 160) extend respectively from the first insertion hole and the second insertion hole toward the first side, and an operation section operable by a finger of a user is provided on the second side.