An automatic analyzer comprising: a suction nozzle; liquid transfer means; a channel connecting the suction nozzle and the liquid transfer means; a flow cell arranged in the middle of the channel; a detector for sample analysis which is arranged in the flow cell; a liquid vessel (404, 405) for storing liquid to be sucked in by the suction nozzle; a dumping part for dumping liquid remaining in the liquid vessel; and a controller; wherein the liquid vessel comprises an overflow part for allowing liquid to overflow from the liquid vessel to the dumping part; characterized by diluting fluid supply means (251, 252) for supplying a diluting fluid to the liquid vessel; wherein the controller is adapted, when the liquid in the liquid vessel is to be discharged from the liquid vessel, to drive the diluting fluid supply means to supply the diluting fluid to the liquid vessel such as to cause remaining liquid in the liquid vessel and the supplied diluting fluid to overflow via the overflow part to the dumping part and to reach a prescribed dilution rate or thinner for the diluted liquid in the liquid vessel, and thereafter to drive the liquid transfer means to have the diluted liquid in the liquid vessel sucked into the flow cell via the suction nozzle and to have it subsequently discharged to the dumping part. a suction nozzle; liquid transfer means; a channel connecting the suction nozzle and the liquid transfer means; a flow cell arranged in the middle of the channel; a detector for sample analysis which is arranged in the flow cell; a liquid vessel (404, 405) for storing liquid to be sucked in by the suction nozzle; a dumping part for dumping liquid remaining in the liquid vessel; and a controller; wherein the liquid vessel comprises an overflow part for allowing liquid to overflow from the liquid vessel to the dumping part; characterized by diluting fluid supply means (251, 252) for supplying a diluting fluid to the liquid vessel; wherein the controller is adapted, when the liquid in the liquid vessel is to be discharged from the liquid vessel, to drive the diluting fluid supply means to supply the diluting fluid to the liquid vessel such as to cause remaining liquid in the liquid vessel and the supplied diluting fluid to overflow via the overflow part to the dumping part and to reach a prescribed dilution rate or thinner for the diluted liquid in the liquid vessel, and thereafter to drive the liquid transfer means to have the diluted liquid in the liquid vessel sucked into the flow cell via the suction nozzle and to have it subsequently discharged to the dumping part. when the liquid in the liquid vessel is to be discharged from the liquid vessel, to drive the diluting fluid supply means to supply the diluting fluid to the liquid vessel such as to cause remaining liquid in the liquid vessel and the supplied diluting fluid to overflow via the overflow part to the dumping part and to reach a prescribed dilution rate or thinner for the diluted liquid in the liquid vessel, and thereafter to drive the liquid transfer means to have the diluted liquid in the liquid vessel sucked into the flow cell via the suction nozzle and to have it subsequently discharged to the dumping part.