The present invention provides a blood analyzer and a blood analyzing method capable of obtaining information regarding B lymphocytes and T lymphocytes without using a fluorescence-labeled antibody. The blood analyzer of the present invention includes a blood specimen supplying portion, a sample preparation portion that prepares a measurement sample without using a fluorescence-labeled antibody by mixing a blood specimen supplied from the blood specimen supplying portion, a hemolyzing agent, and a fluorescent dye that stains nucleic acid, a light source, a first detector that detects fluorescence, a second detector that detects scattered light, and information processing portion that classifies lymphocytes based on the intensity of fluorescence and scattered light, and based on the fluorescence intensity of the classified lymphocytes, obtains information regarding B-lymphocytes and T-lymphocytes.