Abstract: A wavelength tuning apparatus and method that maintain highest efficiency with a single angle manipulation without changing a position of input/output light. For this, the wavelength tuning apparatus and method include a transmission-type diffraction grating and a mirror that are constructed in one-body type so that a light path that enables an optimal efficiency diffraction angle of the diffraction grating can be formed, and rotates the one-body construction to obtain a desired wavelength. Accordingly, efficiency and precision of manipulation and control can be increased, and costs can be reduced.