An automatic analyzer, comprising: a plurality of reaction containers (108, 303) each for containing a reaction solution; a light source for emitting light to be transmitted through the reaction solution; a spectral detector (118, 202) for measuring the transmitted light over an entire area from one end to the other end of each reaction container; and a CPU for calculating a light intensity from the measurement data provided by the spectral detector over an area where the reaction solution exists in each reaction container; a stirring unit for stirring the reaction solution in each reaction container (108, 303); a rotatable reaction disc on which the reaction containers (108, 303) are disposed and a reaction disc motor for driving the reaction disc, wherein the reaction containers are rotatable together with the reaction disc so that they are moved reciprocally between the stirring unit and the spectral detector (118, 202) when the reaction disc motor is controlled by a control unit, and so that the optical axis of the transmitted light is scanned across each reaction container; and a memory for storing the measurement data provided by the spectral detector (118, 202), wherein: the CPU is adapted to extract the light measurement data in an area where the reaction solution exists from the measurement data stored in the memory and to calculate the light intensity transmitted through the reaction solution on the basis of the extracted data, and the CPU is further adapted to analyze the waveform of the light intensity change obtained from the extracted data and thereby to detect insufficient mixture of the reaction solution in the reaction container, such that the reaction solution is stirred again with the stirring unit when the mixing state of a reagent in the reaction solution is insufficient. a plurality of reaction containers (108, 303) each for containing a reaction solution; a light source for emitting light to be transmitted through the reaction solution; a spectral detector (118, 202) for measuring the transmitted light over an entire area from one end to the other end of each reaction container; and a CPU for calculating a light intensity from the measurement data provided by the spectral detector over an area where the reaction solution exists in each reaction container; a stirring unit for stirring the reaction solution in each reaction container (108, 303); a rotatable reaction disc on which the reaction containers (108, 303) are disposed and a reaction disc motor for driving the reaction disc, wherein the reaction containers are rotatable together with the reaction disc so that they are moved reciprocally between the stirring unit and the spectral detector (118, 202) when the reaction disc motor is controlled by a control unit, and so that the optical axis of the transmitted light is scanned across each reaction container; and a memory for storing the measurement data provided by the spectral detector (118, 202), wherein: the CPU is adapted to extract the light measurement data in an area where the reaction solution exists from the measurement data stored in the memory and to calculate the light intensity transmitted through the reaction solution on the basis of the extracted data, and the CPU is further adapted to analyze the waveform of the light intensity change obtained from the extracted data and thereby to detect insufficient mixture of the reaction solution in the reaction container, such that the reaction solution is stirred again with the stirring unit when the mixing state of a reagent in the reaction solution is insufficient. the CPU is adapted to extract the light measurement data in an area where the reaction solution exists from the measurement data stored in the memory and to calculate the light intensity transmitted through the reaction solution on the basis of the extracted data, and the CPU is further adapted to analyze the waveform of the light intensity change obtained from the extracted data and thereby to detect insufficient mixture of the reaction solution in the reaction container, such that the reaction solution is stirred again with the stirring unit when the mixing state of a reagent in the reaction solution is insufficient.