A blood component separation device includes a centrifuge bowl for separating a blood component from blood, a plasma bag for storing a plasma component, a platelet intermediate bag for storing high-concentration platelet liquid having high-concentration of platelets, and a temporary storage bag (also used as a buffy coat bag) for storing low-concentration platelet liquid having low-concentration of platelets. The blood component separation device performs control, from the second cycle onward, to mix the low-concentration platelet liquid stored in the temporary storage bag in the immediately preceding cycle with whole blood to supply the mixed liquid to the centrifuge bowl. An amount of high-concentration platelet liquid to be collected in the platelet intermediate bag in the first cycle is set to be smallest among all cycles, and an amount of high-concentration platelet liquid to be collected in a last cycle is set to be greatest among all the cycles.
