A wavelength reading apparatus for a monochromator comprises a monochromator utilizing a dispersion element for dispersing light in accordance with its wavelengths, a dispersion element driver unit for rotating the dispersion element to effect the tuning wavelength scanning operation of the monochromator and a wavelength counter for adding or subtracting a pulse, which is produced each time when the tuning wavelength of the monochromator changes by a predetermined wavelength increment, depending on whether the wavelength increases or decreases. The wavelength counter is set to a predetermined counting value, in response to a wavelength calibrating pulse produced when the tuning wavelength of the monochromator reaches a predetermined value, so that any counting value of the wavelength counter correctly represents the instant value of the tuning wavelength of the monochromator.