An automatic analyzer controls a sequence including optical measurement and cleaning and includes a discharge mechanism including a discharge nozzle for discharging a liquid into a reaction vessel; and an overflow suction mechanism including an overflow suction nozzle for sucking an overflow amount of the liquid in the reaction vessel. In a liquid discharge step included in a cleaning process and interposed between a preceding step using a detergent and a succeeding blank value measurement step, the automatic analyzer establishes a first state where a lower end of the discharge nozzle is located in a height-wise lower part of the reaction vessel and a lower end of the overflow suction nozzle is located in an upper part of the reaction vessel, and provides control to carry out the discharge of liquid from the discharge nozzle and the suction of the overflow amount of liquid through the overflow suction nozzle.