Provided is a tunable diffraction grating apparatus including: a diffraction grating portion having a diffraction grating with an linearly variable grating interval, the diffraction grating being formed of an elastic member; a drive portion connected to the diffraction grating portion and applying a force to the diffraction grating portion to vary the grating interval; and a controller for controlling the drive portion to adjust the grating interval depending on a specific wavelength input from the exterior.Therefore, the tunable diffraction grating apparatus can vary a grating interval of a diffraction grating using an elastic material so that a signal of a frequency bandwidth of THz can also be used. In addition, it is possible to simplify structure of the apparatus to reduce the manufacturing cost thereof.