The automatic analysis device is provided with (1) a measurement mechanism having a light measuring unit having a reaction container in which the sample is dispensed, a light source which emits light to the reaction container, and a detection unit that detects scattered light from the sample in the reaction container, (2) an amplifier circuit unit having an adder-subtractor that adds or subtracts a correction signal to or from a first measurement signal from the detection unit, and an amplifier circuit which amplifies the output signal by the adder-subtractor at a fixed amplification rate to output a second measurement signal, and (3) an arithmetic operation unit which calculates the correction signal on the basis of a difference between the signal level of the second measurement signal and a target value, and which executes an analysis action based on the second measurement signal after correction by means of the correction signal.