A blood component separation device comprising: a centrifugal separator configured to separate a predetermined blood component from blood; and a container for containing the predetermined blood component centrifugally separated, wherein the blood component separation device is configured to perform (a) centrifugal separation step for introducing whole blood drawn from a donor into the centrifugal separator to separate whole blood into a plurality of blood components, (b) circulation flow step for introducing a predetermined first blood component, among centrifugally separated blood components, separated by the centrifugal separation into the centrifugal separator together with whole blood, (c) circulation/acceleration step, performed after a predetermined amount of the first blood component is separated in the circulation flow step, in which supply of whole blood to the centrifugal separator is stopped to introduce only the first blood component into the centrifugal separator to further circulate the first blood component for a predetermined period of time, and a circulation speed is then increased so that a second blood component is separated by the centrifugal separator and collected, and (d) blood returning step for returning blood components remaining after collecting a predetermined amount of the second blood component in the circulation/acceleration step to the donor, characterized in that the circulation/acceleration step includes a first collecting step for transferring a portion of the second blood component with low-concentration to a temporary storage container and a second collecting step for collecting a portion of the second blood component with high-concentration, the second blood component with low concentration transferred to the temporary storage container is introduced into the centrifugal separator together with whole blood drawn in a following cycle, where the steps (a) to (d) constitute one cycle, and wherein, as for the second collecting step, an amount of the second blood component with high-concentration to be collected in a first cycle is set to be smallest among all cycles, and an amount of the second blood component with high-concentration to be collected in a last cycle is set to be greatest among all the cycles. a centrifugal separator configured to separate a predetermined blood component from blood; and a container for containing the predetermined blood component centrifugally separated, wherein the blood component separation device is configured to perform (a) centrifugal separation step for introducing whole blood drawn from a donor into the centrifugal separator to separate whole blood into a plurality of blood components, (b) circulation flow step for introducing a predetermined first blood component, among centrifugally separated blood components, separated by the centrifugal separation into the centrifugal separator together with whole blood, (c) circulation/acceleration step, performed after a predetermined amount of the first blood component is separated in the circulation flow step, in which supply of whole blood to the centrifugal separator is stopped to introduce only the first blood component into the centrifugal separator to further circulate the first blood component for a predetermined period of time, and a circulation speed is then increased so that a second blood component is separated by the centrifugal separator and collected, and (d) blood returning step for returning blood components remaining after collecting a predetermined amount of the second blood component in the circulation/acceleration step to the donor, (a) centrifugal separation step for introducing whole blood drawn from a donor into the centrifugal separator to separate whole blood into a plurality of blood components, (b) circulation flow step for introducing a predetermined first blood component, among centrifugally separated blood components, separated by the centrifugal separation into the centrifugal separator together with whole blood, (c) circulation/acceleration step, performed after a predetermined amount of the first blood component is separated in the circulation flow step, in which supply of whole blood to the centrifugal separator is stopped to introduce only the first blood component into the centrifugal separator to further circulate the first blood component for a predetermined period of time, and a circulation speed is then increased so that a second blood component is separated by the centrifugal separator and collected, and (d) blood returning step for returning blood components remaining after collecting a predetermined amount of the second blood component in the circulation/acceleration step to the donor, characterized in that the circulation/acceleration step includes a first collecting step for transferring a portion of the second blood component with low-concentration to a temporary storage container and a second collecting step for collecting a portion of the second blood component with high-concentration, the second blood component with low concentration transferred to the temporary storage container is introduced into the centrifugal separator together with whole blood drawn in a following cycle, where the steps (a) to (d) constitute one cycle, and wherein, as for the second collecting step, an amount of the second blood component with high-concentration to be collected in a first cycle is set to be smallest among all cycles, and an amount of the second blood component with high-concentration to be collected in a last cycle is set to be greatest among all the cycles.