A synthesis device comprises a plurality of pipes, a feeding unit, a reaction vessel, and a measurement mechanism. The pipes extend from a plurality of storage containers, respectively, in which a plurality of types of solutions are stored. The feeding unit is configured to feed the solutions in the storage containers through the pipes. The solutions selectively fed from the storage containers are put in the reaction vessel to generate a synthesized product by chemical synthesis. The measuring mechanism is provided between the storage containers and the reaction vessel in a middle of an overall flow path including the pipes, the measuring mechanism being configured to measure the solutions fed to the reaction vessel.