The object of the disclosure is to provide a nano-scale molecular assembly such as a conductive nano-wire. Specifically, there is provided an electrochemical apparatus for forming a molecular assembly, including two electrodes and an electrochemical cell holding an electrolytic solution and the two electrodes, wherein the gap between the two electrodes is from 1 nm to 100 μm, by allowing the electrochemical cell to hold an electrolytic solution containing molecules that is to constitute the molecular assembly, and applying a voltage across the two electrodes in the state wherein the electrolyte and the two electrodes are in contact.