To provide an oscillation device having a long oscillation wavelength in which wavelength variable width is relatively broad and wavelength sweep rate is relatively high. An oscillation device includes a gain medium having a gain with respect to an electromagnetic wave to be oscillated, cavity structures for resonating the electromagnetic wave, and energy injection means and for injecting pumping energy into the gain medium. The gain medium is sandwiched between a first negative permittivity medium and a second magnetic permittivity medium each of which real part of permittivity with respect to the electromagnetic wave is negative. Electric field application means is provided for at least one of the first negative permittivity medium and the second negative permittivity medium to apply an electric field for changing a depletion region formed at a boundary part with the gain medium.