An automatic analyzer comprising: an analytical module (1-7, 2-1) for analyzing a sample and including an incubator disk for supporting multiple reaction cells and for rotating to transport the circumferentially positioned reaction cells to their predetermination positions; and a sample pipetting mechanism configured to aspire a sample held in a sample container and to discharge the sample in an unused reaction cell placed on the incubator disk; a reagent storage unit which stores a plurality of reagent containers; a reagent preparation mechanism which at least has a reagent mixing mechanism for mixing reagents held in the reagent containers; a storage unit which stores priorities of reagent preparation regarding the reagent containers stored in the reagent storage unit; a reagent loader configured to load a new reagent container into the reagent storage unit, wherein the reagent loader is operable to load a new reagent container into the reagent storage unit even during an analysis operation of the automatic analyzer; and a control unit which is configured to store into the storage unit the priority of reagent preparation for each of the reagents held in the reagent containers stored in the reagent storage unit, characterized in that, the control unit is configured to store information about the status of each of the reagents held in the reagent containers stored in the reagent storage unit, wherein the control unit is configured to set the priorities of the reagent preparations based on the information about the status of each of the reagents, the control unit further being configured to determine that the preparation is to be performed by the reagent preparation mechanism for the reagent newly loaded by the reagent loader in preference to, and by temporarily stopping, an operation of the sample pipetting mechanism, if the priority of the reagent newly loaded by the reagent loader stored in the storage unit indicates a high priority of reagent preparation, wherein the reagent preparation mechanism is configured to perform the preparation for the reagent newly loaded into the reagent storage unit in accordance with the determination made by the control unit. an analytical module (1-7, 2-1) for analyzing a sample and including an incubator disk for supporting multiple reaction cells and for rotating to transport the circumferentially positioned reaction cells to their predetermination positions; and a sample pipetting mechanism configured to aspire a sample held in a sample container and to discharge the sample in an unused reaction cell placed on the incubator disk; an incubator disk for supporting multiple reaction cells and for rotating to transport the circumferentially positioned reaction cells to their predetermination positions; and a sample pipetting mechanism configured to aspire a sample held in a sample container and to discharge the sample in an unused reaction cell placed on the incubator disk; a reagent storage unit which stores a plurality of reagent containers; a reagent preparation mechanism which at least has a reagent mixing mechanism for mixing reagents held in the reagent containers; a storage unit which stores priorities of reagent preparation regarding the reagent containers stored in the reagent storage unit; a reagent loader configured to load a new reagent container into the reagent storage unit, wherein the reagent loader is operable to load a new reagent container into the reagent storage unit even during an analysis operation of the automatic analyzer; and a control unit which is configured to store into the storage unit the priority of reagent preparation for each of the reagents held in the reagent containers stored in the reagent storage unit, characterized in that, the control unit is configured to store information about the status of each of the reagents held in the reagent containers stored in the reagent storage unit, wherein the control unit is configured to set the priorities of the reagent preparations based on the information about the status of each of the reagents, the control unit further being configured to determine that the preparation is to be performed by the reagent preparation mechanism for the reagent newly loaded by the reagent loader in preference to, and by temporarily stopping, an operation of the sample pipetting mechanism, if the priority of the reagent newly loaded by the reagent loader stored in the storage unit indicates a high priority of reagent preparation, wherein the reagent preparation mechanism is configured to perform the preparation for the reagent newly loaded into the reagent storage unit in accordance with the determination made by the control unit.