An automatic analyzer comprising: a storage unit adapted to store measurement results of quality control samples differing in their known concentration levels; a calculation unit adapted to calculate at least one of the average, coefficient of variation, and standard deviation, of the measurement results stored in said storage means for each of the plurality of the known concentration levels; a determination unit adapted to compare one of the average, coefficient of variation, and standard deviation, calculated by said calculation means for each of the plurality of known concentration levels of the measured quality control samples, with a previously input or default judgment value; and, if the one of the average, coefficient of variation, and standard deviation exceeds the judgment value for any of the plurality of known concentration levels of the measured quality control samples, to determine variation patterns for each of the plurality of known concentration levels of the measured quality control samples, the variation patterns describing whether the one of the average, coefficient of variation, and standard deviation is decreasing, stable or increasing, and to select the cause of measurement uncertainty on the basis of the determined variation patterns. a storage unit adapted to store measurement results of quality control samples differing in their known concentration levels; a calculation unit adapted to calculate at least one of the average, coefficient of variation, and standard deviation, of the measurement results stored in said storage means for each of the plurality of the known concentration levels; a determination unit adapted to compare one of the average, coefficient of variation, and standard deviation, calculated by said calculation means for each of the plurality of known concentration levels of the measured quality control samples, with a previously input or default judgment value; and, if the one of the average, coefficient of variation, and standard deviation exceeds the judgment value for any of the plurality of known concentration levels of the measured quality control samples, to determine variation patterns for each of the plurality of known concentration levels of the measured quality control samples, the variation patterns describing whether the one of the average, coefficient of variation, and standard deviation is decreasing, stable or increasing, and to select the cause of measurement uncertainty on the basis of the determined variation patterns. to compare one of the average, coefficient of variation, and standard deviation, calculated by said calculation means for each of the plurality of known concentration levels of the measured quality control samples, with a previously input or default judgment value; and, if the one of the average, coefficient of variation, and standard deviation exceeds the judgment value for any of the plurality of known concentration levels of the measured quality control samples, to determine variation patterns for each of the plurality of known concentration levels of the measured quality control samples, the variation patterns describing whether the one of the average, coefficient of variation, and standard deviation is decreasing, stable or increasing, and to select the cause of measurement uncertainty on the basis of the determined variation patterns. <EOS>