Abstract: A polynucleotide synthesizing apparatus comprising a storing section for storing fluid chemicals, including nucleotide reagents, solvents and the like, necessary for polynucleotide synthesis, a reactor in which the fluid chemicals react to effect the polynucleotide synthesis, a fluid supply and discharge arrangement for supplying the fluid chemicals in the storing section to the reactor and for discharging fluid chemicals from the reactor, and a control device for controlling the fluid supply and discharge arrangement. The control device comprises a programmable controller including a storage unit in which supply amount and supply/discharge sequence information for the fluid chemicals is stored. The apparatus also comprises a memory pack comprising semiconductor memory devices in which a control program and/or maintenance program is stored. The memory pack is replaceable with the storage unit of the programmable controller.