An automatic analyzer includes: a reagent mounting unit 103 in which a plurality of reagent bottles 10 are installed when a reagent bottle 10 is loaded into the automatic analyzer; a reagent conveying mechanism 101 including a gripper mechanism 106; and a reagent mounting mechanism 102 for moving the reagent mounting unit 103 between an installation position at which an operator installs the reagent bottle 10 in the reagent mounting unit 103 and a position at which the gripper mechanism 106 grips the reagent bottle 10. It is thereby possible to achieve saving of a mechanism installation space and reduction of the number of constituent components, automatically carry out an operation from opening of the reagent bottle to loading of the reagent bottle into the reagent disk, and alleviate an operator's burden.