An automatic analyzer includes a wastewater suction unit that causes a suction nozzle to suction a reaction wastewater from each of plural reaction vessels transferred to a disposal position, transfers the plural suction nozzles to a cleaning position to make the suction nozzles suction a cleaning liquid, and clean the suction nozzles. The wastewater suction unit includes a pressure detector that is arranged near the suction nozzle in a pipe that guides a negative pressure for suction to each of the suction nozzles to detect pressure in each of the suction nozzles at time of suctioning of the reaction wastewater, a vessel determination unit that determines whether the reaction vessel is present or not at the disposal position, and a clog determination unit that determines whether each of the suction nozzles is clogged or not based on change in pressure in the suction nozzle and presence/absence of the reaction vessel.