An object of the invention is to provide a blood component separation device that can keep the concentration of anticoagulant in a predetermined blood component to a constant level to minimize aggregation of a predetermined blood component (for example, aggregation of platelets). One aspect of the present invention is a blood component separation device that separates the predetermined blood component from the blood drawn from a blood donor while supplying to the blood an anticoagulant for preventing coagulation of the blood, where an anticoagulant ratio, or a ratio of an amount of the anticoagulant supplied in relation to the blood, is set according to a hematocrit value of the blood donor so that a concentration of the anticoagulant in the predetermined blood component becomes a predetermined value.
