A blood analyzer comprising: a specimen preparation means configured to mix a blood sample with a hemolyzing agent which hemolyzes red blood cells and with a fluorescence-labeled antibody reagent which labels a predetermined surface antigen on blood cells, to prepare a first measurement specimen; a flow cell through which the first measurement specimen prepared by the specimen preparation means is caused to flow; a light source means for emitting light to the first measurement specimen flowing in the flow cell; light receiving means for respectively receiving first scattered light, second scattered light, and first fluorescence which are obtained from blood cells in the first measurement specimen as a result of the emission of the light; and a processing means configured to identify and count lymphocytes in the first measurement specimen by using first scattered light information based on the first scattered light and second scattered light information based on the second scattered light, and configured to identify and count blood cells having thereon the predetermined surface antigen in the first measurement specimen by using first fluorescence information based on the first fluorescence, wherein the blood cells having thereon the predetermined surface antigen are CD4-positive T-cells or CD8-positive T-cells, and wherein the first scattered light is forward scattered light, the second scattered light is side scattered light, and the processing means is configured to identify and count the blood cells having thereon the predetermined surface antigen in the first measurement specimen by using second scattered light information based on the side scattered light and the first fluorescence information based on the first fluorescence and thereby differentiating between eosinophils and cells identified by the fluorescent labelled antibody using the second scattered light information. a specimen preparation means configured to mix a blood sample with a hemolyzing agent which hemolyzes red blood cells and with a fluorescence-labeled antibody reagent which labels a predetermined surface antigen on blood cells, to prepare a first measurement specimen; a flow cell through which the first measurement specimen prepared by the specimen preparation means is caused to flow; a light source means for emitting light to the first measurement specimen flowing in the flow cell; light receiving means for respectively receiving first scattered light, second scattered light, and first fluorescence which are obtained from blood cells in the first measurement specimen as a result of the emission of the light; and a processing means configured to identify and count lymphocytes in the first measurement specimen by using first scattered light information based on the first scattered light and second scattered light information based on the second scattered light, and configured to identify and count blood cells having thereon the predetermined surface antigen in the first measurement specimen by using first fluorescence information based on the first fluorescence, the blood cells having thereon the predetermined surface antigen are CD4-positive T-cells or CD8-positive T-cells, and the first scattered light is forward scattered light, the second scattered light is side scattered light, and the processing means is configured to identify and count the blood cells having thereon the predetermined surface antigen in the first measurement specimen by using second scattered light information based on the side scattered light and the first fluorescence information based on the first fluorescence and thereby differentiating between eosinophils and cells identified by the fluorescent labelled antibody using the second scattered light information.