A wavelength-tunable light emitting device includes a substrate having an atomic-scale structure formed on a surface thereof, a needle member for locally applying a voltage through a vacuum space or a transparent insulating member to the substrate to cause a tunnel current to flow through the atomic-scale structure, and a variable-voltage power supply capable of varying voltage applied across the gap between the substrate and the needle member. The gap between the first member and the second member is as close as a few nm in length. A tunnel current flows from the tip of the needle member to the atomic-scale structure when a predetermined voltage is applied across the gap between the substrate and the needle member; and light is emitted from a tunneling region in which the tunnel current flows, because of an optical transition between respective localized states of the substrate and the needle. The wavelength of the light varies when the voltage applied across the gap between the substrate and the needle member is varied.