Without causing an increase in size and complication of an automatic analyzer, the efficiency of washing cuvettes can be increased and the amount of detergent used can be more effectively saved in comparison with known analyzers. In an automatic analyzer in which a sample and a reagent are dispensed into each of a plurality of cuvettes, a resulting reaction solution is mixed under stirring, and reaction states of the mixed reaction solution are measured successively. The automatic analyzer includes a unit for stirring a detergent in the cuvette when the interior of the cuvette is washed with the detergent after measurement of a reaction. The automatic analyzer also includes a control device controlling steps of reaction measurement and washing and incorporating a sequence of stirring in the washing step. A mixing unit for mixing the reaction solution also serves as the unit for stirring the detergent in the cuvette.