Abstract: Provided is an automatic analyzer capable of facilitating maintenance work and adjustment work. Automatic analyzers 100 and 110 are operable by main body software that controls operation of the automatic analyzers 100 and 110 and attached software that is independent of the main body software and is used during maintenance of machines that configure the automatic analyzers 100 and 110. The attached software and the main body software respectively hold specific identification information that specifies an own version. At least one of the attached software and the main body software holds corresponding identification information of a counterpart side software corresponding to current time. Operation units 103 and 113 specify the attached software suitable for the main body software from a plurality of pieces of attached software by comparing the specific identification information and the corresponding identification information.