An automatic analyzer comprising: a reagent dispensing mechanism (14, 17, 30) having a nozzle part for dispensing a reagent; a cleaning water supply part for supplying a cleaning water to the reagent dispensing mechanism (14, 17, 30), the cleaning water supply part including a water supply tank and a liquid delivery pump, the water supply tank storing cleaning water and the liquid delivery pump delivering the cleaning water stored in the water supply tank; a temperature increasing part for increasing the temperature of the cleaning water to be supplied from the cleaning water supply part to the reagent dispensing mechanism (14, 17, 30); and a control unit for controlling the reagent dispensing mechanism, the temperature increasing part, and the cleaning water supply part, the control unit including an input part for inputting analysis request information and a memory part for memorizing the input information, characterized in that the control unit is adapted to determine whether a standby time in which the nozzle part has been cooled by external air is present between dispensing operations based on the analysis request information memorized in the memory part and to control operation of the reagent dispensing mechanism (14, 17, 30) and the cleaning water supply part such that, if the standby time is present between dispensing operations, after the standby time, the cleaning water stored in the water supply tank is delivered by the liquid delivery pump, the temperature of the delivered cleaning water is increased by the temperature increasing part, and the cleaning water of the increased temperature is then supplied to the nozzle part of the reagent dispensing mechanism (14, 17, 30). a reagent dispensing mechanism (14, 17, 30) having a nozzle part for dispensing a reagent; a cleaning water supply part for supplying a cleaning water to the reagent dispensing mechanism (14, 17, 30), the cleaning water supply part including a water supply tank and a liquid delivery pump, the water supply tank storing cleaning water and the liquid delivery pump delivering the cleaning water stored in the water supply tank; a temperature increasing part for increasing the temperature of the cleaning water to be supplied from the cleaning water supply part to the reagent dispensing mechanism (14, 17, 30); and a control unit for controlling the reagent dispensing mechanism, the temperature increasing part, and the cleaning water supply part, the control unit including an input part for inputting analysis request information and a memory part for memorizing the input information, characterized in that the control unit is adapted to determine whether a standby time in which the nozzle part has been cooled by external air is present between dispensing operations based on the analysis request information memorized in the memory part and to control operation of the reagent dispensing mechanism (14, 17, 30) and the cleaning water supply part such that, if the standby time is present between dispensing operations, after the standby time, the cleaning water stored in the water supply tank is delivered by the liquid delivery pump, the temperature of the delivered cleaning water is increased by the temperature increasing part, and the cleaning water of the increased temperature is then supplied to the nozzle part of the reagent dispensing mechanism (14, 17, 30).