To suck a plurality of reagents with the same nozzle by putting an air gap between adjoining reaction reagent and reaction buffer solution to continuously suck with the same nozzle, in sucking the reaction reagent and reaction buffer solution for immunoassay.

A first reagent is sucked by a fixed quantity with one nozzle to lift the nozzle from the vessel of the reagent, and the nozzle is laterally shifted to suck air with a syringe or the like, and a fixed quantity of air gap is put in the tip of the nozzle. The tip of the nozzle is put in a washing tank in the vicinity of the nozzle to clean dirt of the nozzle, the nozzle is moved to the position of a second reagent vessel, and the nozzle is brought down to suck the second reagent by a fixed quantity. After sucking in, the nozzle is again lifted to move it over a reaction tank, and the contents are pushed out to dispense them to the reaction tank. In this case, by washing the interior of the nozzle, even if the operation is repeated, dirt of the first reagent due to the second reagent can be restrained to minimum.