A sample analyzer comprising: a sample preparation section for preparing a measurement sample from an undiluted biological sample and a reagent; mode setting means for setting either a first mode or a second mode as an operating mode; a detector for detecting an analyte contained in the measurement sample prepared by the sample preparation section; a sample supplier for supplying the measurement sample prepared by the sample preparation section to the detector; and a controller in communication with the sample preparation section, the controller being configured to 1) control the sample preparation section so as to obtain a first amount of an undiluted biological sample from a first sample container, and prepare a first measurement sample of a first dilution ratio, when the first mode is set by the mode setting means; and 2) control the sample preparation section so as to obtain a second amount of an undiluted biological sample from a second sample container, the second amount being less than the first amount, and prepare a second measurement sample of a second dilution ratio higher than the first dilution ratio, when the second mode is set by the mode setting means, and configured to control the sample supplier and the detector to detect an analyte contained in a predetermined amount of the first measurement sample when the first mode is set by the mode setting means; and control the sample supplier and the detector to detect an analyte contained in the second measurement sample whose amount is larger than the predetermined amount, when the second mode is set by the mode setting means, wherein the controller is configured to control the sample supplier so as to supply the measurement sample prepared by the sample preparation section to the detector at a predetermined speed, whether the first mode is set by the mode setting means or the second mode is set by the mode setting means. a sample preparation section for preparing a measurement sample from an undiluted biological sample and a reagent; mode setting means for setting either a first mode or a second mode as an operating mode; a detector for detecting an analyte contained in the measurement sample prepared by the sample preparation section; a sample supplier for supplying the measurement sample prepared by the sample preparation section to the detector; and a controller in communication with the sample preparation section, the controller being configured to 1) control the sample preparation section so as to obtain a first amount of an undiluted biological sample from a first sample container, and prepare a first measurement sample of a first dilution ratio, when the first mode is set by the mode setting means; and 2) control the sample preparation section so as to obtain a second amount of an undiluted biological sample from a second sample container, the second amount being less than the first amount, and prepare a second measurement sample of a second dilution ratio higher than the first dilution ratio, when the second mode is set by the mode setting means, 1) control the sample preparation section so as to obtain a first amount of an undiluted biological sample from a first sample container, and prepare a first measurement sample of a first dilution ratio, when the first mode is set by the mode setting means; and 2) control the sample preparation section so as to obtain a second amount of an undiluted biological sample from a second sample container, the second amount being less than the first amount, and prepare a second measurement sample of a second dilution ratio higher than the first dilution ratio, when the second mode is set by the mode setting means, and configured to control the sample supplier and the detector to detect an analyte contained in a predetermined amount of the first measurement sample when the first mode is set by the mode setting means; and control the sample supplier and the detector to detect an analyte contained in the second measurement sample whose amount is larger than the predetermined amount, when the second mode is set by the mode setting means, wherein the controller is configured to control the sample supplier so as to supply the measurement sample prepared by the sample preparation section to the detector at a predetermined speed, whether the first mode is set by the mode setting means or the second mode is set by the mode setting means.