The automatic analyzer includes a storage unit storing the reaction containers of cleaning target by day unit in such a manner that all the reaction containers mounted on a reaction disk are to be cleaning target within a plurality of days, and a control unit exerts a control in such a manner that during an operation state after the sample of analysis object is dispensed to the reaction containers, a sample of analysis object in each of the reaction containers is analyzed, and not the sample but a detergent is dispensed to the reaction containers of cleaning target of an appointed day, the reaction containers of cleaning target of the appointed day being stored in the storage unit, to soak and wash the reaction containers for a certain time.