PROBLEM TO BE SOLVED: To provide an attitude retainer for blood component separation apparatuses that retains an attitude of a blood component separation apparatus capable of improving a collection rate of leukocyte components.SOLUTION: An attitude retainer 16 includes a first attitude retaining member 17 and a second attitude retaining member 18 that are mounted on a blood component separation apparatus 1 to clamp the blood component separation apparatus 1 from both front/rear sides. When the first and second attitude retaining members 17 and 18 are mounted on the blood component separation apparatus 1, the first and second attitude retaining members 17 and 18 are formed with: a first accumulation-part storage unit 25 for storing a volume adjusting mechanism 3, and a first accumulation part 4 a connecting-part storage unit 29a for storing a connecting part 10 formed of a tube with flexibility a third accumulation-part storage unit 27 for storing a third accumulation part 6 a connecting-part storage unit 29b for storing a connecting part 11 with flexibility and a second accumulation-part storage unit 26 for storing a second accumulation part 5, in this order, respectively.
