An automatic analyzer comprising: an analyzing unit including: an analyzing mechanism; and a dispensing reagent cassette storage (28, 29) for storing a reagent cassette for dispensing; a reagent replenishing unit including a replenishing reagent cassette storage for storing in advance a reagent cassette for replenishing to be supplied as the reagent cassette for dispensing, said replenishing unit including a loading port through which a reagent cassette is loaded into the replenishing reagent cassette storage; and means (22, 27) for transferring the reagent cassette for replenishing as the reagent cassette for dispensing from the replenishing reagent cassette storage to the dispensing reagent cassette storage (28, 29), wherein the reagent replenishing unit includes means for reading reagent information affixed to the reagent cassette for replenishing, characterized by comprising: a computer acting as a supply enable/disable determining means for determining whether a newly loaded reagent cassette for replenishing loaded into the replenishing reagent cassette storage can be supplied as the reagent cassette for dispensing; and reagent cassette ejecting means for ejecting from the replenishing reagent cassette storage the reagent cassette for replenishing that cannot be supplied as the reagent cassette for dispensing, wherein said computer is configured to control said reagent cassette ejecting means so as to eject the newly loaded reagent cassette for replenishing from the replenishing reagent cassette storage upon determining that the newly loaded reagent cassette for replenishing cannot be supplied as the reagent cassette for dispensing. an analyzing unit including: an analyzing mechanism; and a dispensing reagent cassette storage (28, 29) for storing a reagent cassette for dispensing; a reagent replenishing unit including a replenishing reagent cassette storage for storing in advance a reagent cassette for replenishing to be supplied as the reagent cassette for dispensing, said replenishing unit including a loading port through which a reagent cassette is loaded into the replenishing reagent cassette storage; and means (22, 27) for transferring the reagent cassette for replenishing as the reagent cassette for dispensing from the replenishing reagent cassette storage to the dispensing reagent cassette storage (28, 29), wherein the reagent replenishing unit includes means for reading reagent information affixed to the reagent cassette for replenishing, characterized by comprising: a computer acting as a supply enable/disable determining means for determining whether a newly loaded reagent cassette for replenishing loaded into the replenishing reagent cassette storage can be supplied as the reagent cassette for dispensing; and reagent cassette ejecting means for ejecting from the replenishing reagent cassette storage the reagent cassette for replenishing that cannot be supplied as the reagent cassette for dispensing, wherein said computer is configured to control said reagent cassette ejecting means so as to eject the newly loaded reagent cassette for replenishing from the replenishing reagent cassette storage upon determining that the newly loaded reagent cassette for replenishing cannot be supplied as the reagent cassette for dispensing. a computer acting as a supply enable/disable determining means for determining whether a newly loaded reagent cassette for replenishing loaded into the replenishing reagent cassette storage can be supplied as the reagent cassette for dispensing; and reagent cassette ejecting means for ejecting from the replenishing reagent cassette storage the reagent cassette for replenishing that cannot be supplied as the reagent cassette for dispensing, wherein said computer is configured to control said reagent cassette ejecting means so as to eject the newly loaded reagent cassette for replenishing from the replenishing reagent cassette storage upon determining that the newly loaded reagent cassette for replenishing cannot be supplied as the reagent cassette for dispensing.