1. A blood cell analyzer comprising: a detector for detecting predetermined component of leukocytes contained in a specimen; and a controller, including a memory under the control of a processor, the memory storing: correlation information relating to the correlation between leukocyte distribution data and either stab neutrophil or segmented leukocyte classification data; and instructions enabling the processor to carry out operations, comprising: (a) obtaining leukocyte distribution data of a subject based on the detection results of the detector; (b) obtaining the stab neutrophil or segmented leukocyte classification data based on the correlation information and the leukocyte distribution data of the subject; and (c) outputting the obtained stab neutrophil or segmented leukocyte classification data.