We report the application of an intermolecular interaction design for organic conductor crystals with a high conductance to a molecule-electrode design for a high single-molecule conductance by using dithiol and diselenol terthiophenes. We found that dithiol and diselenol single-molecule junctions show the highest single-molecule conductance among single-molecule junctions with Au-S and Au-Se bonds, and that diselenol single-molecule junctions have a higher single-molecule conductance than dithiol ones. We demonstrate that replacing S atoms with Se atoms is a promising molecule-electrode bonding design for a high single-molecule conductance.