In a reaction between a biomolecule and a radioactive agent precursor, the amount of a component of a radioactive agent precursor before the reaction and the amount of a component contained in a reaction mixture in a reaction process in which the reaction is performed at a predetermined biomolecule concentration are measured, a reaction rate constant is calculated from the information of the obtained amounts of the components, a reaction rate constant when the biomolecule concentration is changed is calculated, a reaction time, a specific radioactivity, and a radioactivity level of an objective substance at each biomolecule concentration are predicted, and synthesis is performed under a reaction condition under which the highest specific radioactivity is obtained among the reaction conditions satisfying the synthesis requirements.
