Disclosed is a blood analyzer that includes: a sample preparation unit configured to mix a blood specimen and a fluorescent dye for staining nucleic acid to prepare a measurement sample; a light receiver configured to receive fluorescence and scattered light that are generated by light being applied to the measurement sample prepared by the sample preparation unit; and a controller programmed to determine whether or not infection with Plasmodium has occurred, on the basis of a value representing variation of a distribution of first particles in a range where single-ring form of red blood cells appear, the range where single-ring form of red blood cells appear being identified according to fluorescence intensities and scattered light intensities obtained by processing of signals from the light receiver.