A blood analysis method comprising steps of: preparing a first measurement sample containing a blood sample and a cationic surfactant and a second measurement sample containing said blood sample, the same cationic surfactant as said cationic surfactant and a staining agent; generating first fluorescent information and at least two types of first scattered light information from said first measurement sample and generating second fluorescent information and second scattered light information from said second measurement sample; classifying white blood cells in said first measurement sample into at least four groups of monocytes, neutrophils, eosinophils and a group of the others on the basis of said first fluorescent information and said two types of first scattered light information generated from said first measurement sample; and classifying blood cells in said second measurement sample into malaria-infected red blood cells and a group of the others on the basis of said second fluorescent information and said second scattered light information generated from said second measurement sample, wherein the cationic surfactant is: i) an alkyl trimethyl ammonium salt, the number of carbons of the alkyl group of which is at least twelve and not more than eighteen, and wherein the concentration of the cationic surfactant in the first measurement sample is at least 0.62 mM and not more than 2.15 mM, or ii) an alkyl trimethyl ammonium salt, the number of carbons of the alkyl group of which is at least eight and not more than ten, and wherein the concentration of the cationic surfactant in the first measurement sample is 2.15 mM or more. preparing a first measurement sample containing a blood sample and a cationic surfactant and a second measurement sample containing said blood sample, the same cationic surfactant as said cationic surfactant and a staining agent; generating first fluorescent information and at least two types of first scattered light information from said first measurement sample and generating second fluorescent information and second scattered light information from said second measurement sample; classifying white blood cells in said first measurement sample into at least four groups of monocytes, neutrophils, eosinophils and a group of the others on the basis of said first fluorescent information and said two types of first scattered light information generated from said first measurement sample; and classifying blood cells in said second measurement sample into malaria-infected red blood cells and a group of the others on the basis of said second fluorescent information and said second scattered light information generated from said second measurement sample, wherein the cationic surfactant is: i) an alkyl trimethyl ammonium salt, the number of carbons of the alkyl group of which is at least twelve and not more than eighteen, and wherein the concentration of the cationic surfactant in the first measurement sample is at least 0.62 mM and not more than 2.15 mM, or ii) an alkyl trimethyl ammonium salt, the number of carbons of the alkyl group of which is at least eight and not more than ten, and wherein the concentration of the cationic surfactant in the first measurement sample is 2.15 mM or more. i) an alkyl trimethyl ammonium salt, the number of carbons of the alkyl group of which is at least twelve and not more than eighteen, and wherein the concentration of the cationic surfactant in the first measurement sample is at least 0.62 mM and not more than 2.15 mM, or ii) an alkyl trimethyl ammonium salt, the number of carbons of the alkyl group of which is at least eight and not more than ten, and wherein the concentration of the cationic surfactant in the first measurement sample is 2.15 mM or more.