An automatic analyzer has a transport device which includes a specimen rack gripping mechanism that grips the specimen rack on a first transport path on which the specimen racks are transported by the specimen rack being sandwiched between gripping plates from both sides of flanks in the transport direction to transport the specimen rack along the first transport path and a gripping width controller that controls a distance between the gripping plates of the specimen rack gripping mechanism in accordance with a width of the specimen rack. Accordingly, an automatic analyzer capable of transporting a plurality of types of the specimen racks while suppressing an increase in size of the apparatus and also an increase in cost can be provided.