A method for measuring a biological sample, comprising steps of: preparing a measurement sample by damaging cell membranes of erythrocytes and mature leukocytes in a biological sample, substantially not damaging cell membranes of hematopoietic progenitor cells in the biological sample, shrinking the damaged erythrocytes, and staining nucleic acid in the damaged mature leukocytes with a fluorescent dye by mixing a surfactant for damaging cell membranes of erythrocytes and mature leukocytes, a solubilizing agent for shrinking the damaged erythrocytes, a fluorescent dye for staining a nucleic acid, and a biological sample for 3 seconds to 5 minutes, wherein the surfactant is a polyoxyethylene non-ionic surfactant represented by the formula: R 1 -R 2 -(CH 2 CH 2 O) n -H, wherein R 1 is a C 9 to C 25 alkyl, alkenyl or alkynyl group, R 2 is -O-, -COO- or and n is an integer of 10 to 40; irradiating cells in the measurement sample with light; obtaining forward scattered light intensity, side scattered light intensity and fluorescence intensity from the irradiated cells; specifying hematopoietic progenitor cells based on the obtained forward and side scattered light intensities and the obtained fluorescence intensity, comprising a first preparation of a first two-dimensional scattergram and a second preparation of a second two-dimensional scattergram; and counting the specified hematopoietic progenitor cells; characterized in that: the first two dimensional scattergram has the forward and side scattered light intensities on the two axes and displays hematopoietic progenitor cells and platelet aggregate discriminated by the forward and side scattered light intensities; and the second two dimensional scattergram has the forward or side scattered light intensity and the fluorescent intensity on the two axes and displays hematopoietic progenitor cells, granulocytes, lymphocytes, and monocytes discriminated by the forward or side scattered light intensity and the fluorescence intensity. preparing a measurement sample by damaging cell membranes of erythrocytes and mature leukocytes in a biological sample, substantially not damaging cell membranes of hematopoietic progenitor cells in the biological sample, shrinking the damaged erythrocytes, and staining nucleic acid in the damaged mature leukocytes with a fluorescent dye by mixing a surfactant for damaging cell membranes of erythrocytes and mature leukocytes, a solubilizing agent for shrinking the damaged erythrocytes, a fluorescent dye for staining a nucleic acid, and a biological sample for 3 seconds to 5 minutes, wherein the surfactant is a polyoxyethylene non-ionic surfactant represented by the formula: R 1 -R 2 -(CH 2 CH 2 O) n -H, wherein R 1 is a C 9 to C 25 alkyl, alkenyl or alkynyl group, R 2 is -O-, -COO- or and n is an integer of 10 to 40; irradiating cells in the measurement sample with light; obtaining forward scattered light intensity, side scattered light intensity and fluorescence intensity from the irradiated cells; specifying hematopoietic progenitor cells based on the obtained forward and side scattered light intensities and the obtained fluorescence intensity, comprising a first preparation of a first two-dimensional scattergram and a second preparation of a second two-dimensional scattergram; and counting the specified hematopoietic progenitor cells; the first two dimensional scattergram has the forward and side scattered light intensities on the two axes and displays hematopoietic progenitor cells and platelet aggregate discriminated by the forward and side scattered light intensities; and the second two dimensional scattergram has the forward or side scattered light intensity and the fluorescent intensity on the two axes and displays hematopoietic progenitor cells, granulocytes, lymphocytes, and monocytes discriminated by the forward or side scattered light intensity and the fluorescence intensity.