A blood sample analyzer capable of operating in a first measuring mode for measuring a blood sample and a second measuring mode for measuring a blood sample, comprising: a sample provider for providing a blood sample; a common reagent provider for providing a common reagent used in the first measuring mode and the second measuring mode; a special reagent provider for providing a staining liquid as a special reagent used in the second measuring mode; a mode selector for selecting one of the first measuring mode and the second measuring mode; a measuring section for measuring the blood sample; and wherein in the first measuring mode, the sample provider and the common reagent provider operate so as to make a first mode sample comprising the blood sample and the common reagent, and the measuring section operates so as to measure the first mode sample, and in the second measuring mode, the sample provider, the common reagent provider and the special reagent provider operate so as to make a second mode sample comprising the blood sample, the common reagent and the special reagent, and the measuring section operates so as to measure the second mode sample, characterised in that: the common reagent is a hemolyzing reagent, in that the measuring section comprises a light source for irradiating light to a flow of one of the first mode sample and the second mode sample, and a light detector for receiving the light irradiated on the flow, in that the light detector comprises a scattered light detector for detecting scattered light generated by irradiating the light from the light source to the flow, and a fluorescent light detector for detecting fluorescent light generated by irradiating the light from the light source to the flow, and in that, in the first measuring mode, the measuring section measures the first mode sample by the scattered light detector so as to calculate a number of white blood cells contained in the first mode sample, and in the second measuring mode, the measuring section measures the second mode sample by the scattered light detector and the fluorescent light detector so as to calculate a number of white blood cells contained in the second mode sample and classify the white blood cells contained in the second mode sample into predetermined classifying items. a sample provider for providing a blood sample; a common reagent provider for providing a common reagent used in the first measuring mode and the second measuring mode; a special reagent provider for providing a staining liquid as a special reagent used in the second measuring mode; a mode selector for selecting one of the first measuring mode and the second measuring mode; a measuring section for measuring the blood sample; and wherein in the first measuring mode, the sample provider and the common reagent provider operate so as to make a first mode sample comprising the blood sample and the common reagent, and the measuring section operates so as to measure the first mode sample, and in the second measuring mode, the sample provider, the common reagent provider and the special reagent provider operate so as to make a second mode sample comprising the blood sample, the common reagent and the special reagent, and the measuring section operates so as to measure the second mode sample, characterised in that: the common reagent is a hemolyzing reagent, in that the measuring section comprises a light source for irradiating light to a flow of one of the first mode sample and the second mode sample, and a light detector for receiving the light irradiated on the flow, in that the light detector comprises a scattered light detector for detecting scattered light generated by irradiating the light from the light source to the flow, and a fluorescent light detector for detecting fluorescent light generated by irradiating the light from the light source to the flow, and in that, in the first measuring mode, the measuring section measures the first mode sample by the scattered light detector so as to calculate a number of white blood cells contained in the first mode sample, and in the second measuring mode, the measuring section measures the second mode sample by the scattered light detector and the fluorescent light detector so as to calculate a number of white blood cells contained in the second mode sample and classify the white blood cells contained in the second mode sample into predetermined classifying items.