An method is offered which can clean the nozzles of a reaction cuvette wash unit. A first detergent is put in first reagent containers located on a first reagent turntable. A computer controller drives a first reagent pipette to aspirate the detergent from the first reagent containers and to deliver the detergent into reaction cuvettes. The controller drives a reaction turntable to bring each reaction cuvette holding the detergent therein to the reaction cuvette wash unit. The controller drives the reaction cuvette wash unit to aspirate the detergent from inside the reaction cuvettes using reaction cuvette wash nozzles to thereby clean the wash nozzles. A second detergent is then used to clean the nozzles.