A sample analyzer configured to selectively operate in a first measurement mode or a second measurement mode, comprising: a sample preparation section configured to prepare a measurement sample from an undiluted biological sample and a reagent; a detector configured to measure the measurement sample; a sample supplier for supplying the measurement sample to the detector; and a controller configured to: in the first measurement mode, control the sample preparation section to prepare a first measurement sample of a first dilution ratio; in the second measurement mode, control the sample preparation section to prepare a second measurement sample of a second dilution ratio higher than the first dilution ratio; control the sample supplier to supply the first measurement sample to the detector (D3, S302) in the first measurement mode, and to supply the second measurement sample to the detector (D3, S502) in the second measurement mode; start measurement of the measurement sample (S304, S504), in the first measurement mode, stop supplying of the first measurement sample after a first period has elapsed, and in the second measurement mode, stop supplying of the second measurement sample after a second period has elapsed, wherein the second period is longer than the first period; and control the sample supplier to supply the first measurement sample and the second measurement sample to the detector at the same speed. a sample preparation section configured to prepare a measurement sample from an undiluted biological sample and a reagent; a detector configured to measure the measurement sample; a sample supplier for supplying the measurement sample to the detector; and a controller configured to: in the first measurement mode, control the sample preparation section to prepare a first measurement sample of a first dilution ratio; in the second measurement mode, control the sample preparation section to prepare a second measurement sample of a second dilution ratio higher than the first dilution ratio; control the sample supplier to supply the first measurement sample to the detector (D3, S302) in the first measurement mode, and to supply the second measurement sample to the detector (D3, S502) in the second measurement mode; start measurement of the measurement sample (S304, S504), in the first measurement mode, stop supplying of the first measurement sample after a first period has elapsed, and in the second measurement mode, stop supplying of the second measurement sample after a second period has elapsed, wherein the second period is longer than the first period; and control the sample supplier to supply the first measurement sample and the second measurement sample to the detector at the same speed. in the first measurement mode, control the sample preparation section to prepare a first measurement sample of a first dilution ratio; in the second measurement mode, control the sample preparation section to prepare a second measurement sample of a second dilution ratio higher than the first dilution ratio; control the sample supplier to supply the first measurement sample to the detector (D3, S302) in the first measurement mode, and to supply the second measurement sample to the detector (D3, S502) in the second measurement mode; start measurement of the measurement sample (S304, S504), in the first measurement mode, stop supplying of the first measurement sample after a first period has elapsed, and in the second measurement mode, stop supplying of the second measurement sample after a second period has elapsed, wherein the second period is longer than the first period; and control the sample supplier to supply the first measurement sample and the second measurement sample to the detector at the same speed.