A method to inexpensively and efficiently produce conductive materials on the surface of which a nano-level fine structure is formed includes surface modification including immersing a stable anode electrode and a workpiece as a cathode electrode, the workpiece including a conductive material with a work surface, in an electrolytic solution, then applying a voltage not less than a first voltage and less than a second voltage between the stable anode electrode and the workpiece as the cathode electrode immersed in the electrolytic solution, thereby modifying the work surface, the first voltage being a voltage corresponding to a current value that is ½ of the sum of a first maximum current value appearing first in a positive voltage region and a first minimum current value appearing first in the positive voltage region with respect to voltage-current characteristics of a surface modification treatment system, the second voltage exhibiting a complete-state plasma.