This invention provides an abnormally-activated-cell apheresis-therapy apparatus for inhibiting the onset of or treating leukemia by removing abnormally activated cells, specifically abnormally activated leukocytes or leukemia progenitor cells, from blood. Said abnormally-activated-cell apheresis-therapy apparatus, which is an abnormally-activated-leukocyte apheresis-therapy apparatus that removes abnormally activated cells such as leukemia cells from blood, said cells having been made identifiable via high-concentration accumulation of protoporphyrin IX, is provided with the following: a blood-collection line, one end of which is provided with a needle for blood collection； a centrifugal separator that separates out a leukocyte fraction from blood sent down the blood-collection line； a cell sorter that removes abnormally activated cells from the separated-out leukocyte fraction； a light-exposure device that exposes the normal leukocyte fraction resulting from the removal of the aforementioned abnormally activated cells to light of a prescribed wavelength； and a return line that returns, to the patient, the normal leukocyte fraction and a return fluid comprising the blood components other than the leukocyte fraction.
