A near-field interaction control element includes a near-field optical
waveguide containing particles formed of a metal, a metal anion or a
metal cation with a diameter of 0.5 nm or more and 3 nm or less and a
dielectric constant of -2.5 or more and -1.5 or less, an electron
injector/discharger injecting or discharging an electron into or from the
particles contained in the near-field optical waveguide to vary a
dielectric constant of the near-field optical waveguide, a near-field
light introducing part introducing near-field light into the near-field
optical waveguide, and a near-field light emitting part emitting the
near-field light having guided through the near-field optical waveguide.