A blood component collection system (10) includes a first internal pressure calculation unit (110) adapted to calculate a first internal pressure of a first pressed portion (60) using first calibration curve data (118), a second internal pressure calculation unit (112) adapted to calculate a second internal pressure of a second pressed portion (62) using second calibration curve data (120), and a correction unit (114) adapted to correct the first calibration curve data (118) in a manner so that, during a blood returning operation, the first internal pressure calculated by the first internal pressure calculation unit (110) becomes equal to the second internal pressure calculated by the second internal pressure calculation unit (112).