An automatic analyzer including a sampler for delivering given amounts of samples into reaction vessels arranged along a reaction line, a reagent tray for holding a plurality of reagents, a reagent delivery device for delivering given amounts of reagents into the reaction vessels, and a measuring device for measuring test liquids in the reaction vessels, the reagent tray includes a turn table, a plurality of divided trays detachably provided on the turn table and having a plurality of compartments, and a plurality of reagent containers containing the reagents and being installed into compartments of divided trays. An identification code is provided on respective divided trays for identifying the division information, and a reagent identifying label is provided on a respective reagent container for identifying a respective reagent. The reagent delivery device includes a first detector for detecting said identification code on the divided tray and a second detector for detecting said reagent identification label. In this manner any desired reagent container can be indexed into a reagent sucking position in accordance with the division information, reagent information and a test item to be analyzed. The number and size of the compartments in the divided tray are set such that a plurality of reagent containers having different sizes can be effectively set on the divided tray, and thus a large number of reagent containers having different volumes may be efficiently arranged on the reagent table to perform rapid and adequate analysis and make unnecessary frequent exchange of reagent containers.