PURPOSE: To realize a spectral measuring apparatus whose sensitivity is high and whose stray light is low in a single-dispersion-system spectroscope without spoiling its dispersion efficiency.

CONSTITUTION: A sharp-cut filter 12 which cuts off light at a specific wavelength λ0 or lower is installed at the front of an incident slit 3 for a spectroscope 2, and light 1 to be measured is guided into the spectroscope 2 through the sharp-cut filter 12. When the set wavelength of the spectroscope 2 is at λ0 or lower, the light which comes out from a radiant slit 9 is a stray-light component which is generated by the light, to be measured, at the wavelength λ0 or higher. The output of a detection system at this time is recorded as stray light, the stray-light component is subtracted from a signal obtained from the detection system within the range of a wavelength to be measured, and a spectral output which has removed the stray light can be obtained.