The automatic analysis device includes an analysis unit that corrects, based on a measured value at the time of a first light amount measurement with water dispensed in the reaction cell before the sample is dispensed therein; a measured value at the time of a second light amount measurement after the sample and a preprocessing reagent are dispensed into the reaction cell; a liquid amount in the reaction cell at the time of the second light amount measurement; and a liquid amount in the reaction cell at the time of a third light amount measurement after the reaction reagent has been dispensed into the reaction cell and before the reaction reagent and the substance to be measured react with each other.