An automatic analyzer provided with a roller and a reagent container shoulder presser at the position where an operator inserts a reagent container into the automatic analyzer. The reagent container is pushed while the lid of the reagent container is made to touch the upper side of the roller and the shoulder presser is made to touch the shoulder of the reagent container, and the application of upward force to the lid causes the lid of the reagent container to be half open, after which the reagent container is inserted in the analyzer.