1. A blood stain sample imaging apparatus that detects improper staining comprising: a light source for irradiating a stained blood sample that includes white blood cells having stained nucleuses; a white blood cell detector for detecting the white blood cells from the stained blood sample; an imaging section for imaging the stained blood sample to generate a plurality of cell images each of which includes at least one of the white blood cells detected by the white blood cell detector; and a processor and a memory storing a computer program that configures the processor to perform operations comprising: identifying a nucleus area of each the white blood cells based on the cell images; classifying the white blood cells into a plurality of types; and determining a staining abnormality by: determining white blood cell nucleus luminance values of each of the identified nucleus areas; generating an average value of the white blood cell nucleus luminance values; comparing the average value of the white blood cell nucleus luminance values with a stored acceptable range; and outputting an alert indicating a staining abnormality of the stained blood sample to a user of the apparatus in response to a comparison result outside the stored acceptable range.