It is necessary to efficiently agitate a small amount of sample (such as blood) and reagent (such as diluted solution) in a short time with a dispensing probe having a constant tube inner diameter. An automatic analysis device, by a dispensing probe, executes an aspiration step of aspirating a reagent from a reagent vessel; a first dispensing and aspiration step of dispensing a first liquid amount of the aspirated reagent to a reaction vessel and aspirating, from the reaction vessel, a second liquid amount of a mixed liquid obtained by mixing the reagent and the sample in the reaction vessel; and a final dispensing step of dispensing the aspirated mixed liquid and the reagent in a predetermined dispensing amount. A first liquid amount Va is less than a predetermined dispensing amount Vdil.