An analyzer for analyzing a biological sample, comprising: a) a measurement specimen preparation section adapted to prepare a measurement specimen by using a reagent and the biological sample; b) a flow cell adapted to flow the measurement specimen prepared by the measurement specimen preparation section; c) an irradiator adapted to irradiate the measurement specimen flowing through the flow cell with a light; d) a first light receiving section adapted to receive a light from the measurement specimen and convert the received light into an electrical signal; e) an analysis section adapted to analyze the measurement specimen based on the electrical signal output by the first light receiving section; f) an input section adapted to input specification whether or not to perform each of a plurality of measurement modes in relation to measurement targets; and wherein g) when a first measurement mode in relation to a first measurement target and a second measurement mode in relation to a second measurement target different from the first measurement target have been specified for an analysis of the biological sample, the measurement specimen preparation section prepares a first measurement specimen corresponding to the first measurement mode by using a part of the biological sample and prepares a second measurement specimen corresponding to the second measurement mode by using a part of the biological sample; characterized by h) a first control unit (501 h) adapted to control the irradiator (501 d) to irradiate with a light of an intensity corresponding to the specified measurement mode; wherein i) the first control unit automatically controls, in the first measurement mode, the irradiator to irradiate a light of a first intensity corresponding to the first measurement mode on the first measurement specimen flowing through the flow cell, and automatically controls, in the second measurement mode, the irradiator to irradiate a light of a second intensity corresponding to the second measurement mode on the second measurement specimen flowing through the flow cell, the second intensity being different from the first intensity; wherein j) the input section accepts the specification of the measurement mode from among a white blood cell differentiation measurement mode in which measurement target is white blood cell and a platelet measurement mode in which measurement target is platelet; and k) the first control unit controls the irradiator to irradiate smaller intensity of the light for measurement in the white blood cell differentiation measurement mode than an intensity of the light for measurement in the platelet measurement mode. a) a measurement specimen preparation section adapted to prepare a measurement specimen by using a reagent and the biological sample; b) a flow cell adapted to flow the measurement specimen prepared by the measurement specimen preparation section; c) an irradiator adapted to irradiate the measurement specimen flowing through the flow cell with a light; d) a first light receiving section adapted to receive a light from the measurement specimen and convert the received light into an electrical signal; e) an analysis section adapted to analyze the measurement specimen based on the electrical signal output by the first light receiving section; f) an input section adapted to input specification whether or not to perform each of a plurality of measurement modes in relation to measurement targets; and wherein g) when a first measurement mode in relation to a first measurement target and a second measurement mode in relation to a second measurement target different from the first measurement target have been specified for an analysis of the biological sample, the measurement specimen preparation section prepares a first measurement specimen corresponding to the first measurement mode by using a part of the biological sample and prepares a second measurement specimen corresponding to the second measurement mode by using a part of the biological sample; h) a first control unit (501 h) adapted to control the irradiator (501 d) to irradiate with a light of an intensity corresponding to the specified measurement mode; wherein i) the first control unit automatically controls, in the first measurement mode, the irradiator to irradiate a light of a first intensity corresponding to the first measurement mode on the first measurement specimen flowing through the flow cell, and automatically controls, in the second measurement mode, the irradiator to irradiate a light of a second intensity corresponding to the second measurement mode on the second measurement specimen flowing through the flow cell, the second intensity being different from the first intensity; wherein j) the input section accepts the specification of the measurement mode from among a white blood cell differentiation measurement mode in which measurement target is white blood cell and a platelet measurement mode in which measurement target is platelet; and k) the first control unit controls the irradiator to irradiate smaller intensity of the light for measurement in the white blood cell differentiation measurement mode than an intensity of the light for measurement in the platelet measurement mode.